Is it from a desktop? Also what make is the computer?
Try scanning the computer using the Crucial website
www.crucial.com and it will give you upgrade options for it.
You can either let is scan it or you can go through the drop-down menu to select the manufacturer and model, etc. If you get types of RAM upgrade then you can take the model numbers and see if you can get it cheaper elsewhere, but you might just end up saving a couple of quid to be honest. You could check the Kingston Value RAM that was going cheap on Play.com Just try searching for 'Kingston RAM' as there were some 1GB sticks for about £12 each the other week. Get two and you've doubled the RAM in the machine for under £25, the Crucial upgrade kit will probably be just under £30 so it's up to you if you want to pay the extra couple of quid for Crucial RAM or not.