Which services can I stop/disable?

http://majorgeeks.com/page.php?id=12 is another good explanation (used to be my favorite when it was still 'live' on line).

Last thing I'd say is - make sure you set them to manual before you disable them, especially if you're unsure.
That way if it 'has' to start, it still can...

Go to Winpatrol.com and download the program. It will show which items are in the start up mode. I would then disable 5 at a time from your list, and wait a day to see if there are any malfunctions. This is what I do.

d_may - you've pointed out the one I linked to....blackviper is no longer online (not sure if it'll ever be back up again :(
But the link I posted is a cached version of it...

Thank-You sirbounty,

The following is a list of Services that you can Disable on most systems for increased performance:

 Alerter
 Distributed Link Tracking Client
 Help and Support - (If you use Windows Help and Support leave this enabled)
 Indexing Service
 IPSEC Services
 Messenger - (Shoot the Messenger and installing SP2 will disable this)
 Portable Media Serial Number - (Leave enabled for use with Security Dongles)
 Remote Registry Service
 Secondary Logon
 SSDP Discovery Service - (Unplug n' Pray will disable this)
 Telnet
 Upload Manager
 Wireless Zero Configuration - (If you are on a wireless network leave this enabled)

The following is a list of Services that should always be set to Automatic:

 Automatic Updates - (Required by Windows Updates)
 Background Intelligent Transfer Service - (Required by Windows Updates)
 COM+ Event System - (Required by BootVis and other Applications)
 Cryptographic Services - (Required to confirm the signature of Windows system files, Protected Root Services and Key Services)
 DCOM Server Process Launcher - (Required by Disk Defragmenter)
 DHCP Client - (Required for Cable/DSL connections and Routers)
 DNS Client - (Improves Internet Performance)
 Event Log - (Required by Windows and cannot be Stopped)
 Logical Disk Manager - (Required to manage and update your Harddrives)
 Network Connections - (Required by Network Connections)
 Plug and Play - (Required by your System Hardware, Never Disable This!)
 Print Spooler - (Required by Printers)
 Protected Storage - (Required to protected sensitive data and to prevent access by unauthorized services, processes, or users.)
 Remote Procedure Call (RPC) - (Required by Windows, Never Disable This!)
 Security Accounts Manager - (Required to store security information for local user accounts)
 Security Center - (Notifies you of you Firewall and AntiVirus Status)
 Shell Hardware Detection - (Required by the AutoPlay feature)
 System Event Notification - (Required by various Applications)
 System Restore Service - (Required by the System Restore feature)
 Task Scheduler - (Required by the Windows Prefetcher, BootVis and Norton AV, Never Disable This!)
 Themes - (Required by the new look of Windows XP)
 Windows Audio - (Required for Sound)
 Windows Management Instrumentation - (Required by Windows, Never Disable This!)

Notes - Windows Updates can enable services that you have previously disabled. Check which services are running after a future Windows Update is completed. If applications stop working after using this guide it is usually due to being to aggressive with disabling services. Enable the services you disabled one at a time until the application works. In the future leave this service on automatic. If you run into any problems set all services back to their Defaults and start over.

d_may

Even though the majorgeeks page sirbounty posted is from the same origin, I just thought I'd add this.  You can get the original stuff from the blackviper page in the web archives here:

http://web.archive.org/web/20050220021935/www.blackviper.com/WinXP/servicecfg.htm
http://web.archive.org/web/20050220020020/www.blackviper.com/WinXP/service411.htm