Hey, I need a little help with choosing RAM.

Currently I have somewhere around 700mb RAM, and I'm not really sure what type it is... But it's in 2 sticks. I have 2 more slots available I believe. The current RAM is also at different speeds, which causes problems I heard.

Anyways, I'd like to get 2GB RAM. I really need it for audio stuff, and games. But I'm not sure what to get, and if I should just chuck out my current RAM for it, as it's different speeds.

I'd also like to get it at a decently cheap price, so nothing fancy. Just something that does the job properly. And if anyone in Australia knows where I can order it, please tell.