does it help me ?

[FusionX]

you need to buy the same u have now fex. DDR2 400mhz

download everest if u dont know what u have

[NordFront]

open your taskmanager (ctrl + alt + del), on the right bottom of the taskmanager window you got "Used Memory: xxx"
check & remember how much is in use
then you open KO, start to login blabla, firstoff go to a empty place like eslant entrace, then switch out to taskmanager (alt + tab) and check again how much memory is in use, afterwards you go to moradon or w/e you claim to have laggs and as soon it starts to freeze/lagg you tab out and check used memory again.

IF the amount of used memory comes close or higher then 480 while playing you defenatly need more RAM.
if you know where the RAM sticks on your mainboard are placed open your PC, take it out and bring it to the shop, theres usually a nice sticker on the ram card with all informations they need to know to give you a matching new ram card..

[Hypnotize]

i have bought 1g of ram now i go 1.512 ram and i have the same problem
didnt help me