Internet Slow On One PC Not The Others?

we recently decided to put wireless in the house, and the problems really started from there. The internet was really slow, especially considering the bandwidth was upgraded as well (since my dad thought the internet seemed slower on wireless, though I thought it was expected). I have this really old laptop with Vista/Fedora dual boot and the internet works fine there; my dad's laptop also works fine, but the home's desktop (which has the wireless adapter) is incredibly slow. I've tried uninstalling the LinkSys wireless manager and letting windows handle it, but no luck there. I thought maybe it was cluttered with stuff or maybe it was infected but Avira and SuperAntiSpyware only find a couple of cookies which they delete at the end of their scan.

I should mention that with the upgrade in bandwidth we got a new router (or modem? whatever); I can't quite remember if the internet was slow before or after, but it was put up after the wireless.