WinXP computer not able to browse shared...

Alright, I have a client with a Linksys network hub with a USB printer port connected to:

1) A new Windows XP machine
2) An older, Win98SE machine
3) A laptop running WinME
4) [space reserved for future printer]

The older one and the laptop used to be on a network, working fine, and then a new computer was added, with a professional installation to the network. Everything worked fine.

The suddenly, (apparently) randomly, the Windows machine stopped sharing it's files. Nothing browsing in, nothing browsing out.

This is where I was requested to help. A bit of fiddling around, and I found out that the Advanced Networking Package from Microsoft has been known to be screwy with networks - not letting random computers connect to the internet, etc. etc. I uninstall that.

Now, both the laptop and the win98 machine can browse through the newer computer's shared files. But nothing out - whenever I go to a folder in "My Network Places", any folder times out - server not found. I go through Workgroup>Computer>Folder in Network Neighbourhood, still timeout.

Note: The internet, has always worked through this time.

I rebooted twice, then suddenly I can get through to the laptop's files! Huzzah! I try the other computer - nothing. Huh? I try the first computer - still nothing. Hmm.

Any ideas?