One computer with slow net connection on network

I have a network with a number of computers all wired to a router. All of the computers except one have no problem loading web sites. That other computer will remain at the ‘Waiting for www.whatever.com’ stage for several minutes before finally loading the page. This occurs both with IE (6 and 7) and Firefox. No other computers are experiencing this.

I’ve scanned for spyware etc using Spybot and cleaned the registry with JV16 Powertools, but it has made no difference. Neither has defrag or freeing more disk space. This computer is running XP Pro SP2. Any suggestions would be welcome.