If you get the throughput you expect with Firefox, then clearly Explorer is broken and needs a repair installation. But if it doesn't, then you've got some more homework to do. Off the top of my head, it could be:
1. The laptop is using a sketchy patch cord or a questionable network run. Physical layer problems cause retransmission, which appears as slowness at the application layer. You might also examine the laptop's Ethernet jack for debris.
2. Some fool tweaked the registry's MTU settings in an attempt to speed up the network connection. XP is self-tuning.
3. Some of the popular malware that's come out in the last few months slipped by some antivirus/antispyware programs. New versions of Kryptic and Olmarik are recent such examples, both of which silently hijack your internet connection with 20-40 http and https connections to foreign servers for god-knows-what. That will suck the bandwidth right out of a connection. I reccomend that you download the
Sysinternals Suite (or use the
online version if you're short on space). Run tcpview and procexp to see if anything's crackin' in that arena.
4. And have you thrown out or disabled any Add-on bloat in the browser (Tools | Manage Add-ons)?
