Internet trouble with one XP SP3 machine on a wired/wireless network with 5
machines (XP, Vista Biz, Vista Home, Win 7). This machine is wired to Belkin
wireless router and has spotty internet connection. IE8 sluggish loading and
running. Loading tabs sometimes take forever, sometimes takes no time at
all. All other machines networked with each other and surfing the web
without problems. I've narrowed the problem down to this machine because it
behaves the same way if I bypass the router and connect it directly to the
modem.

I have/have tried:
All recent XP updates
Disabling Add ons
Registry cleaner
Resetting TCP/IP settings
Optimizing TCP/IP settings with DrTCP
WinSockFix
LSP Fix
Creating and setting registry keys:
NegativeCacheTime
NetFailureCacheTime
NegativeSOACacheTime
Uninstalling/reinstalling network adapters
Testing each of two built in adapters
Swapped out cables
Swapped cables among different different router jacks
Reset IE8 to defaults
Ran MalwareBytes
AVG Free Scan
AdAware
Spybot

Incidentally, programs that update themselves aren't having any problem
connecting to their servers

Can anyone think of anything else I might check before I re-install an OS?

Many thanks!

Ripper