I've been having some serious trouble with my 15" Flat Panel iMac. On occasion I get really bizarre screen artifacts and garbage in various applications. I dont know what the problem is - I did an archive and install and erased all of the preferences in my home directory to no avail. The problem is not frequent but it is extremely annoying to say the least. What do you think, does this look like a hardware problem or a software problem? I've attached a screen shot of the problem. thanks!