First, all this assumes we are talking about a Windows network.
Okay, can you ping a machine at work once you are connected with the VPN? If you can, then you just need to setup an lmhosts file that will map the computer names of the machines you need to connect to with an ip address.
You'll find a sample in (assuming WinXP):
C:\WINDOWS\system32\drivers\etc\lmhosts.sam
(If Win2K replace WINDOWS with WINNT)
Edit that file and save it as "lmhosts" no .sam, or .txt, etc.
There are still lots of reasons things could be failing, don't know enough about your network...
Oh, and \\IP-Address will not work, Windows only works with computer names.