I have 2 needs.
1) My main computer blue screens every couple of hours. I'm sure it's corrupt memory. The thing is under warranty but there's a few reasons I'd rather do it myself... a) I've got too much stuff on it. b) They've messed it up before twice and if they fix it something else will go wrong and c) they wouldn't know what a computer was if they used one daily. So any size of RAM really, I need at least 512Mb in total so what's the best way to do it? It's possible that just one of the sticks is corrupt, so once I've checked I might be able to get just the one 256 stick.
2) A PC which isn't used much has 256Mb of shared memory. Because it's shared I only ever get 196Mb out of it, and seen as most programs need 256Mb I'd be best off getting a 256Mb stick to accompany the one which is there, then it'll be a bit faster.
So that's a possibility of 2x 256Mb, 3x 256Mb or 1x 256Mb and 1x 512Mb. I should really have checked exactly what I needed before posting but I really just want to know what it'll cost so I can make some decisions on what to do.