Firstly, I replacedd the IDE cable to the HDD, and then switched some stuff around in the process (HDD is on IDE-0 and DVD+-RW and DVD-rom are on IDE-1 now, they were the other way around before) That really helped. AND when I did this, it decided my DVD+-RW drivers needed redone, so I let it.
Then, I went to Panda Antivirus's FREE online scan, and it informed me that I had some Gaobot Gen Worm or something, but that it had fixed it.
Hopefully my problem's fixed now and the nasty slowdown with intermittent other errors will stay away. :)
BTW, I'm rather annoyed that I needed to use IE to virus-scan my comp, apparently FireFox doesn't like it, and just shows error messages in the window instead of a 'scanning' screen. :/