DHCP and DNS address lists are out of sync

Hi Experts,

My company has managed printer accounting software operating on all our client systems.  Intermittently, and seemingly without any pattern, users are being sent other user's print confirmation dialogs.  When I log onto the DHCP server to investigate their DNS addresses and DHCP leases I discover that in many cases the DNS address don't match the DHCP lease address.

My server topology (as relates to this issue) is as follows:
DHCP server (also secondary DNS server) with Server 2K3
Primary DNS server with Server 2K3
Print Server (also support DNS server) with Server 2K3

On a subnet within my domain (second site):
DHCP and DNS server with Server 2K3

I have had outside contractors involved in this issue, and they have made a number of changes to DNS address scavenging settings, lease request settings/timeouts, etc.  Just yesterday we changed the primary DNS server to be our DHCP server under the assuption it may be possible that client computers are booting up and receiving their DNS addresses from the support DNS servers before checking their leases with the DHCP server.

What else am I missing?  I read some on this topic (very helpful stuff found at http://www.windowsnetworking.com/articles_tutorials/Troubleshooting-Basic-TCPIP.html ) and am wondering (though it has been dismissed somewhat by the contractors) whether my router may be acting as a "rogue" DHCP server.  If so, how can I ensure that it doesn't interfere with my network?