File extraction errors

Dell Dimension 8300 system.

User was having issues with the computer randomly giving her blue screens, whether it be at bootup or during working. Sometimes she could go for a long time with no problem and then one day it would eventually blue screen again. Messages and stop codes on the blue screens varied.

Last week she tried downloading the trial versions of Adobe Indesign and Pagemaker. When trying to run both of those installers, during the file extraction, it would give a corrupt file error. Even re-downloading didn't help.
I copied the files to a different computer, same error. I then re-downloaded the same files at the other computer and they were fine.

So with those problems I decided I would just format it and reinstall Windows XP. The format and install went fine, as did all the driver installs.

When I put in my XP service pack 2 udpate CD, during its file extraction, I got a corrupt file error. I put the disc in the other optical drive and ran it again and it was fine.

Later I was running the Office XP sp1 update; the cdrom copies a file to the hard drive. When I ran the file from the hard drive, and then put in the office disc like it asked, it also eventually gave a corrupt file error. I put the office disc in the other drive and ran it again, but it also gave me an error, though it was slightly different and happened much sooner, it was the same thing, corrupt file (it said could be due to low memory or corrupted CAB).
So I rebooted and ran it again and it worked fine.

I have installed a handful of software and only the windows and office service packs gave me any issues. I haven't seen any blue screens yet either. But the service pack corrupt files during extraction raise a red flag for me since that was happening before the format with those Adobe downloads.

I booted from the dell resource cd and went into the diagnostics and ran the memory test.
Right off the bat it failed the data bus stress test, but it passed the long MATS and March A tests just fine. I ran the data bus stress test by itself 5 more times and it passed all of those attempts.

I left it running the hard drive diagnostic. It had already passed most of those tests, and was doing the verify test when I left it for the day.

Does it make sense to anyone what would cause the corrupt file errors during data extraction in those few select cases that it happened? Should I try to get the memory replaced? Any other hardware that might be at fault?