About 1/3 of web sites load really slow on my desktop connected to wifi, but not on my iPod Touch connected to the same wifi

Solution 1:

Turns out it was the drivers for the network card. Even though I'd installed the correct drivers and verified them, and they worked for a while, every time Windows update ran it would download install incorrect drivers that it thought were "better". Because they mostly worked I didn't notice the problem right away. I didn't notice the issue in Device Manager either when I went to verify and update my drivers manually, because the mis-identified device looks similar to the correct one.

I uninstalled the incorrect drivers and the problem went away, but Windows keeps trying to download the incorrect drivers whenever it updates, and the "correct" drivers have some oddities on Windows 7 anyway, so eventually I just bought a new network adapter. This solved the problem permanently.