I take it you don't have service pack 2 installed on your XP. cuz resetting the winsocks usually works for cases like this. resetting the winsocks with out SP2 requires the CD.
If there is any way that you could get the IP's of the sites you are trying to access, try to ping those sites by the IP. If you can ping by IP but not name it's probably a DNS issue and you can type that sites IP in your browser and it should come up. You'd have to contact your ISP for their DNS #'s
Other things it could be....Maybe that site has some sort of heafty flash or something none of your browsers support. Or if you are running behind any firewalls try turning those off. Try to turn off any anti-anything programs you are running and trying. Many programs have firewalls in them that you may not realize.
Well i do tech support for a living, so i'm trying. but usually if people are not getting certain pages...it's either winsocks, firewalls, or some other computer issue. Also make sure your friends going to those sites are getting updated versions and they aren't pulling that site from the cache.