corrupt data on samsung HD501LJ

I have a Samsung SpinPoint T166 500GB SATA2 16MB 7500RPM (HD501LJ)
It is plugged in a gigabyte GA-965P-S3 (rev. 1.0) mainboard, for which I upgraded the bios and installed the latest chipset drivers. I’m running windows XP and Vista.
I’ve been experiencing data corruption, when I copy some data from some other hd (or from itself, or download from internet) to this hd and verify the data (using accompanying .svf files) the data is a lot of the time corrupt, not always though, only when I’ve written a few GB of data to it (so it seems).
The HD doesn’t get very hot, I checked this with the freeware program HD tune, the temp stays around 30-35 degrees centigrade. I’ve run spyware doctor, avg virus scan, and mcafee virus scan; nothing noteworthy found.
I get the same problem in xp and vista (which i very recently installed, so i guess the chance for viruses or ad- or spyware a few).
I’ve checked Samsungs site for diagnostic programs and found the ultimate boot cd to have these programs (shdiag and HUTIL), I’ve run them, but they indicate there is no problem. I’ve noticed these programs write very little to the HD.
Some extra observation: when I copy a collection of .rar files with .sfv file, and keep copying them over and over again until the files all get through the check, then some of the time, when I recheck the .svf later, the files are corrupt, and some of the time they are not. Sometimes they are corrupt, and a few days later when a rerecheck them they are fine again. (When exactly they are corrupt or not i haven’t been able to pinpoint, but i guess it is worst when I’ve been doing I/O operations for a minute or so)

My question is, if I send this hd back, do they to the same test (shdiag and HUTIL), then conclude there is nothing wrong and send it back?

How can I make sure its the HD and not some other piece of hardware/software that is causing this corruption (i have an IDE disc, and 2 USB external drives (2 lacies, one with exactly the same HD in it that all run without problems). So im looking for additional test i can perform.