Dell XPS 400 freezes intermittently

I have a dell xps 400 that freezes up every 2 seconds or so for about a second. The mouse freezes, audio skips, the hard drive freezes (from watchin the light and listening to it). At first I thought it was a goof in XP so I did a complete reinstall of XP. While installing updates after the reinstall, it started doing it again. The only thing that cures it is a reboot. I also noticed that when it does this, I loose my ethernet connection. The lights are still on on the port and the "network connections" box shows its still active, but there is no internet or local connection.

Then I started suspecting a hard drive failure since it started doing it only with heavy HDD usage (Installing updates and copying files back onto the PC). I ran both the short and long DST test on the HDD using SeaTools. It passed both times. I have ran Burn In Test multiple times at 98% on the CPU, RAM, Graphics (2D and 3D), HDD, and Network. The PC passes every test every time with NO errors.

I ran a Hardware monitor while the freezing occurs and temps are reading normal (no overheating). I am going to run a PSU test this afternoon. I am also going to try another stick of RAM just to be sure but to me its looking like a Motherboard especially. What do you guys think??