New notebook can't see network

I just got a new notebook and am having the same troubles, getting the "MSHOME is not accessible..." when trying to view the network. I will call the computers 600M, 5100, desktop1 and desktop2 for simplicity's sake, with 600M being my new computer. Here are all the gory details:

1. We're using a Belkin 802.11b wireless router as a network hub between the computers and the cable modem.
2. All PC's have Windows XP Home on them
3. I have WEP enabled and am able to connect to the Internet with 600M
4. I am not able to see any of the other networked computers with 600M, however
5. All the other computers can see 600M just fine and I can copy files to its shared drive
6. I have run the Network Connection Wizard on all computers involved
7. I have double-checked computer names and workgroup name (MSHOME) on all computers
8. I have checked Services to be sure both Computer Browser and TCP/IP NetBIOS Helper are on
9. I have enabled/disabled Window Firewall - no luck
10. I do have File/Printer sharing exceptioned out on Windows firewall
11. I have tried closing Avast Antivirus on all systems - no change

Any ideas on how to get these computers to play nicely together? I can't think of anything else right now -- ask me if you need more info.