I suspect that it is not an issue with the speed and the amounts of data comming into the computer, since a dialup connection takes in the same amount, just at a lower rate.
I suspect it was how the connection was set up..
Go to Start> Control Panel> "Internet Options"
Select "Connections"
Click "LAN Settings"
and select "Automatically detect proxy settings"
Click OK
Delete any dialup connections on the dialup list (That is if you dont use them anymore)
Still not working?
It could be a problem with the connection protocols that Windows uses to connect to the Internet, FTP, HTTP, FILE, etc
How you fix that?
I have no idea, but something I learned from Patio:
Click Start> Run
Type:
sfc /scannow
Press ENTER
(Have your XP Installation disk ready)