SupraMayro

I not looking for upgrade to ddr2 or4 I just need to know what type if ddr2 I need to huy

I have on my computer 2gb ddr2 ram it says on it pc6400u 800hz rx8 1.8v if I says it correctly,now I wanna by another one,so every ddr2 ram I'll buy will work with it fine?? How do I know which one to buy??, please guide how to know this things there is a tons of types, like pc5400 and pc6400(without U in the end) and rx8 and without,there is a lot of numbers and letters on it and I don't even know what it means, I find out this information of the motherboard if it helps:Identifyingnumber:LMGUPXDSystem Model(Name):7298WD9 - (I think this is the model number)Manufacturer: LENOVO