Question regarding the different "types" of DDR RAM

[Strychnine]

Okay, so I read the FAQ at the top but didn't seem to find anything directly relating to my confusion, which is, I'm looking to go from 2gig to 4gig of ram, however I'm unsure if my computer takes PC2-5300, PC2-6400, or PC2-8500+ (going from the listings on the OCUK website), or does this not matter? I just wanted to get things clear before I make a purchase so I'm not messing around sending things back because I purchased the wrong type.

Thanks in advance.

 

[Reality|Bites]

What are your system specs?

 

[Strychnine]

Edit: I spoke to a friend of mine who wasn't available last night, he cleared it all up for me, feel free to lock/delete