The stuttering basically only occurs when I run anything that's semi CPU-intensive. Nothing too hard on it, but when I have Winamp playing a song while I load Firefox, the music will stutter during the loading. For things like torrents, as long as I'm uploading or downloading with a torrent, it will stutter about every 5-10 seconds. The mouse also gets choppy, and my CPU usage jumps to 75%-100% during the duration of the stuttering. (Note: this is on my old 150GB hard drive. The 250GB only stutters when loading things like a game or something.)
I've definitely run out of ideas. Aside from replacing my CPU, but I ran Knoppix (Linux LiveCD) off of my CD-ROM drive and didn't find a stuttering problem there. Although, I couldn't find anything to run that was very CPU-intensive in Knoppix, so maybe that's why? However, I think Knoppix proves that it isn't a RAM problem, considering that the entire OS runs off the RAM. I also ran tests on the RAM, and everything seemed normal.
I'm tired of spending money on things that aren't fixing the problem. I really don't want to buy a new CPU, as it would obviously cost even more than I've spent on a PSU and motherboard.
Also, something weird that I've noticed is that when I run off of my 250GB, the stuttering isn't nearly as bad as the 150GB. I think this has something to do with the fact that it's newly formatted and doesn't have much on it right now. I've already formatted it about 5 times because it seems like the more things I put on this hard drive, the worse the problem gets. However, even with only Windows XP loaded onto it, I can still get it to stutter. It's just that it isn't as bad, and it's harder to get it to stutter in the first place.
And yes, I've updated all of my motherboard drivers. The sound I'm using is onboard, but I don't think it's a sound-related problem because the CPU usuage shoots up. I think the stuttering in the sound is just one of the results of the actual CPU stuttering.