[c-nsp] Good way of finding unauthorized network elements/

[Scott Granados]

Hi all
I have a general question.  I have a network consisting of about 20 access 
switches and 2 core switches.  We have 3 access points that we manage but 
think someone might have brought in a linksys or DLink consumer device and 
plugged in.  (users, can't live with em, can't shoot em)
Is there a tool or good method that could scan the arp table and look for 
Manufacturor ID bits so I could see roughly what's attached where?  Are 
there better tools in general or better methods of finding rogue elements 
that people may attach?
Any pointers would be appreciated.

Thanks
Scott