Shoutbox

okz, fist of all

In RAM you should always consider quantity AND speed
quantity is measured in MB/GB and speed in MHz
(speeds in brackets are DDR speeds)

Most prolly your motherboard will support upto 1GB sticks, but you should check it out.

Second you should see what your processor clock rate is, so this is the maximum speed that the RAM will work, so if your processor is running at lets say 133.3 MHz (266.6 MHz), the maxinmun speed that RAM DDR will work is 266 MHz... even though you put higher speed RAM like DDR 200 MHz (400 MHz)

you should also check if your mother board supports dual channel RAM, well i think newer mobos support this, (my crappy one doesnt)

Anyway two slots will be of brown color and other two in blue color, not that color matters but you'll see that there are two pairs, of different colors.
This indicates that mobo supports dual channel ram...

Now if your motherboard supports duall channel RAM this means that it is better to have 2 memory sticks than one

Now if you have a single  DDR 1GB (400 MHz) stick then you have the same quantity but at lower speed aka (400 MHz)

Which means that 2 x DDR 512 MB (400 MHz) will give you a spead of 800MHz because data is tranfered direcltly to each RAM stick
So you have same quantity but double speed

Now you can see that having two sticks if way better than 1 IF the motherboard supports dual channel RAM.

Hope all the above makes sence and help you, in your decision.