It seems to be any application I run. Browsing, flash video, music, Word... you name it.
I can only run for about 25 to 30 minutes and then I am rebooting again. Here is something else that is weird. One night I was importing a CSV file into Excel (hard since i don't know how to use a computer

) It was a pretty big project so I was saving often while I setup the CSV. I would freeze up and force a reboot. But my CSV file did not reflect the changes that had been saved prior to the freeze. This happened a few times. So I saved my file and did a normal restart. This time the files were actually saved.
I tried to get some help at the Mac store in Annapolis but getting crapped on for an hour wasn't fixing the problem. I did suspect some hardware issue but things go great while I'm in Windows. Now, I am not a fan of Vista at all but it runs fantastic on the iMac. That is why I am thinking of just using all the HDD for it.
But, I bought a Mac because of all the great features in it. But if I freeze up all the time I really can't use them.