Oatman, if it is a Dell laptop then you need a ram module which is only available from Dell, I bought the very thing last year and had no problems. If you have a P.C. then you may be able to use any supplier online.
I've bought 512MB RAM on-line from Crucial UK. Highly recommended, especially after I bought a supposedly matched pair of Dimms (which weren't) from a shop which shall remain nameless.
You do need the name and model number of your motherboard to buy from Crucial but they have an on-line configurator and give you all the RAM options for that MB. Good prices too!
Thanks Demon...I'll check them out. I've found a few but by the time I've added P&P and on one site a £5 charge for orders under £49, I might as well buy locally.