Is it possible to dedicate a CPU core to xenserver VM?

Looks like the info you provided is for Vmware.  I am running Xenserver 5.5.

How do I set affinity on Xenserver?

Check out this forum post:

http://forums.citrix.com/thread.jspa?threadID=247486&tstart=0

Roger's a good guy... :)  You have to do the pinning of a CPU on the command line.  There is no way to do it in the GUI.  General thought behind this is that you should use all the resources available, and let XenServer decide how to best allocate those resources.  if you REALLY want to trump those decisions, Roger details how to do it in the above forum post.

Here's another good forum post:

http://forums.citrix.com/thread.jspa?threadID=245034&tstart=0

and the associated doc:

http://docs.vmd.citrix.com/XenServer/5.0.0/1.0/en_gb/reference.html#cli-xe-commands_vm

I really don't want to do it this way but we are force to in certain situation with Oracle licensing.  Oracle's licensing model is based on # of CPU's as opposed to vCPUs'.  Therefore, In order to meet the licensing terms, I need to be able to lock a VM into x number of cores.

I took a look at the post you gave.  I don't have xm commands in Xenserver 5.5  Only xe commands and apparently there is NO 'vcpu-pin' command in the xe command set.  Here are all of the commands for xe:

Is it called something else now?

# xe help --all
Usage: xe <command> [-s server] [-pw passwd] [-p port] [-u user] [-pwf password-file]
  [command specific arguments]

To get help on a specific command: xe help <command>

Full command list
-----------------
    host-backup, host-bugreport-upload, host-call-plugin
    host-compute-free-memory, host-cpu-list, host-cpu-param-get
    host-cpu-param-list, host-crashdump-destroy, host-crashdump-list
    host-crashdump-param-get, host-crashdump-param-list
    host-crashdump-upload, host-data-source-forget, host-data-source-list
    host-data-source-query, host-data-source-record, host-disable
    host-dmesg, host-emergency-ha-disable
    host-emergency-management-reconfigure, host-enable, host-evacuate
    host-forget, host-get-server-certificate, host-get-system-status
    host-get-system-status-capabilities
    host-get-vms-which-prevent-evacuation, host-is-in-emergency-mode
    host-license-add, host-license-view, host-list, host-logs-download
    host-management-disable, host-management-reconfigure, host-param-add
    host-param-clear, host-param-get, host-param-list, host-param-remove
    host-param-set, host-power-on, host-reboot, host-restore
    host-retrieve-wlb-evacuate-recommendations, host-send-debug-keys
    host-set-hostname-live, host-shutdown, host-shutdown-agent
    host-sync-data, host-syslog-reconfigure

    vm-cd-add, vm-cd-eject, vm-cd-insert, vm-cd-list, vm-cd-remove, vm-clone
    vm-compute-maximum-memory, vm-copy, vm-crashdump-list
    vm-data-source-forget, vm-data-source-list, vm-data-source-query
    vm-data-source-record, vm-destroy, vm-disk-add, vm-disk-list
    vm-disk-remove, vm-export, vm-import, vm-install, vm-list
    vm-memory-shadow-multiplier-set, vm-migrate, vm-param-add
    vm-param-clear, vm-param-get, vm-param-list, vm-param-remove
    vm-param-set, vm-pause, vm-reboot, vm-reset-powerstate, vm-resume
    vm-retrieve-wlb-recommendations, vm-shutdown, vm-snapshot
    vm-snapshot-with-quiesce, vm-start, vm-suspend, vm-uninstall, vm-unpause
    vm-vcpu-hotplug, vm-vif-list

    bond-create, bond-destroy, bond-list, bond-param-get, bond-param-list
    cd-list, console-list, console-param-add, console-param-clear
    console-param-get, console-param-list, console-param-remove
    console-param-set, diagnostic-compact, diagnostic-db-log
    diagnostic-db-stats, diagnostic-gc-stats, diagnostic-license-status
    diagnostic-timing-stats, diagnostic-vdi-status, diagnostic-vm-status
    event-wait, log-get, log-get-keys, log-reopen, log-set-output
    message-create, message-list, message-param-get, message-param-list
    network-create, network-destroy, network-list, network-param-add
    network-param-clear, network-param-get, network-param-list
    network-param-remove, network-param-set, patch-apply, patch-clean
    patch-destroy, patch-list, patch-param-clear, patch-param-get
    patch-param-list, patch-pool-apply, patch-precheck, patch-upload
    pbd-create, pbd-destroy, pbd-list, pbd-param-add, pbd-param-clear
    pbd-param-get, pbd-param-list, pbd-param-remove, pbd-param-set, pbd-plug
    pbd-unplug, pif-forget, pif-introduce, pif-list, pif-param-add
    pif-param-clear, pif-param-get, pif-param-list, pif-param-remove
    pif-param-set, pif-plug, pif-reconfigure-ip, pif-scan, pif-unplug
    pool-certificate-install, pool-certificate-list, pool-certificate-sync
    pool-certificate-uninstall, pool-crl-install, pool-crl-list
    pool-crl-uninstall, pool-deconfigure-wlb, pool-designate-new-master
    pool-disable-external-auth, pool-dump-database, pool-eject
    pool-emergency-reset-master, pool-emergency-transition-to-master
    pool-enable-external-auth
    pool-ha-compute-hypothetical-max-host-failures-to-tolerate
    pool-ha-compute-max-host-failures-to-tolerate, pool-ha-disable
    pool-ha-enable, pool-initialize-wlb, pool-join, pool-list
    pool-param-add, pool-param-clear, pool-param-get, pool-param-list
    pool-param-remove, pool-param-set, pool-recover-slaves
    pool-restore-database, pool-retrieve-wlb-configuration
    pool-retrieve-wlb-diagnostics, pool-retrieve-wlb-recommendations
    pool-retrieve-wlb-report, pool-send-test-post
    pool-send-wlb-configuration, pool-sync-database, pool-vlan-create
    session-subject-identifier-list, session-subject-identifier-logout
    session-subject-identifier-logout-all, sm-list, sm-param-get
    sm-param-list, sr-create, sr-destroy, sr-forget, sr-introduce, sr-list
    sr-param-add, sr-param-clear, sr-param-get, sr-param-list
    sr-param-remove, sr-param-set, sr-probe, sr-scan, sr-update, subject-add
    subject-list, subject-list, subject-param-clear, subject-param-get
    subject-param-list, subject-remove, task-cancel, task-list
    task-param-get, task-param-list, template-export, template-list
    template-param-add, template-param-clear, template-param-get
    template-param-list, template-param-remove, template-param-set
    template-uninstall, update-upload, user-password-change, vbd-create
    vbd-destroy, vbd-eject, vbd-insert, vbd-list, vbd-param-add
    vbd-param-clear, vbd-param-get, vbd-param-list, vbd-param-remove
    vbd-param-set, vbd-plug, vbd-unplug, vdi-clone, vdi-copy, vdi-create
    vdi-destroy, vdi-forget, vdi-import, vdi-introduce, vdi-list
    vdi-param-add, vdi-param-clear, vdi-param-get, vdi-param-list
    vdi-param-remove, vdi-param-set, vdi-resize, vdi-snapshot, vdi-unlock
    vdi-update, vif-create, vif-destroy, vif-list, vif-param-add
    vif-param-clear, vif-param-get, vif-param-list, vif-param-remove
    vif-param-set, vif-plug, vif-unplug, vlan-create, vlan-destroy
    vlan-list, vlan-param-get, vlan-param-list