Indications:
Accessing network shares of file is very slow
Copying network shares in vista computer is slow or stopped.
Resolving computer or network resource names with DNS taking time or not working.
and some more……

Reason :
This is because of some new network functions in Vista. Microsoft tried some different technology in vista network to make things easy, but finally it failed. It is not a common problem for all vista computers, if your computer has latest service packs, patches and hot fixes, you may not face these above problems.