It depends on how much RAM each SLOT can handle...So this is one step in from how much your mobo can handle as a whole.
If your motherboard can support like 1.5 or 2gb of RAM and you only have 2 slots then that means each slot can handle up to 1gb RAM stick
So basically as long as the slot can handle 512mb or more it will work.
You'd have to go to the manufacturer website or your manual to find out how much each slot can hold, BUT like I said if you know your computer can handle atleast 1gb and you only have two slots then that RAM will work in it.