A very old board to say the least.
Supports up to 4GB memory size. Dual channel DDR333/400MHz. Memory modules.
So four 1Gb memory sticks in each of the four memory slots of the board.
Try not to mix them it`s a bad idea. If you do make sure each stick matches in Speed.
DDR 333Mhz or DDR 400Mhz, and the timing values of the memory also match on all of the memory sticks Eg: 4-4-4-12.
Here have a check on the specs, click on the link bellow to check out what I have just told you ok.
Should work ok with two 512Mb sticks and two 1Gb sticks in the other two free slots of the motherboard. http://uk.msi.com/product/mb/RS480M2.html#/?div=Detail