I was at a clients the other night fighting and fighting with a networking issue.  I finally changed a setting on the router and poof! it worked.  It was rather stupid, I had a second router being used as an AP (Access Point) and set it up as so.  Well, I switched a setting from "Gateway" to "Router" mode and that did it.
I will say though that I HATE post 2k networking... XP was "OK", once you disabled "simple file sharing"... but with win2k, it just WORKED!   Vista and 7 are even worse.