VPN issues

I am a newbie student who needs to setup my laptop to access the company network from home. Here are the scenarios:

1.Work has a PC hardwired into a wireless modem/wireles router (Linksys WRT54G).

2. I have a wireless laptop which I have setup a VPN on to connect to company network.

3. I setup the Windows XP VPN at work and I was able to connect, but when I got home I could not connect. I get an Error 800.

I can always connect at work.

I would appreciate any help I can get.