Do I have a memory error?

Hi :DI got my PC four months ago. I have occasionally noticed errors like the ones pictures below:http://www.atomic-album.com/showPic.php/23...Memoryissue.jpghttp://www.atomic-album.com/showPic.php/23...mory_error2.jpg(I had just finished using my Lexmark printer, hence the LX---.exe)My PC: P4 3.0E, FSB 800 1MB cache, ATI Radeon 9200SE 128MB, 512MB DDR, Win XP Home Ed, HD 70% empty. I have tried a memory testing program, but it doesn't come back with any errors. I only tested it for an hour, though. The program's documents say that it can take days before a memory error is found, if at all ....What should I do? :-hmmm