Im having a simular issure..
I have 3 pc's on my home network and all 3 see each other "I can transfer files from one to another" and all 3 and connect to the internet and internet game servers but 1 of the 3 systems will not see the other 2 when trying to start a LAN game.
The 3 systems connect through a linksys router and all are running MS XP Pro service pack 3
Ive tried a number of games without success
UT3, UT goty, serious sam, AVP 2