not passing http traffic

Recently my computer stopped passing http traffic correctly, I've
reinstalled XP sp2 to no avail.

When the computer first boots up it browses the internet with no
problem, after a short time it stops passing http traffic. All other
traffic including https, imap, pop, ssh etc... are passed without
problem. I ran netstat and found that my browser process (or any
process trying http) is listed as SYN_SENT. It almost seems to me that
the computer has a limited number of hooks to take http traffic on and
when those fill up it won't recieve anything back from the webserver.

Does anyone have any ideas?