Trouble is you might flash the bios and screw up the machine. I'm not being critical here but it does seem you don't know a great deal about pc's, and by that I mean bios, hardware etc. The one secret with RAM is dont mix odd ram sticks, always put in 2 of the same ie 2 x kingston 1gb 5200 speed or whatever, persoanlly I would stick in 2 x 1gb and save all the hassel of possibly corrupting your windows install, which by the way I very much doubt PC World will cover. There is an old computer proverb which I always used in my shop, "If it aint broke don't fix it". I promise you, you will not notice any difference between 2 and 4 gb apart from the cost of buying it!!! PC world are great at selling things but then I'm afraid it's a visit to your local PC shop.