Identifying RAM

[Thing]

I'm something of a hardware newbie but I agreed to get my brother some extra RAM for his birthday. Only problem is I don't know what he's got now.

We opened up his case and he's got 3 free slots for RAM to go in and his current 512 MB stick says "Samsung 334" on the side.

I just need to find a cheap-ish way to get it up to 1 GB.

 

[Quixote]

I'd use the free program CPU-Z to get more info on the RAM, then try to match it as near as poss.
You'll be looking at another 512 stick & to be honest as long as it's the same speed & type it'll probably work. There can be disadvantages to using RAM from different manufactures but it's less than 5% speed difference usually.
Another way is to try & identify the motherboard then use that to find what RAM you should be looking at.