I have yet to have severe upload/download problems with a 2.4GHz P4 home-brew system running either Windows 98SE or Windows XP SP1a. The only issue I used to have was on Windows 98SE when I task switched prior to the progress bar starting on a download. I have not seen this recently on Windows XP.
Heck, I'm even connected through a USB 1.0 hub with no problems. Even connected to the PC directly (using motherboard USB connectors) running USB 2.0, I still have no problems.