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.
If you have two sticks of 512mb, you need to check there speed. DDR 333 Mhz or DDR 400Mhz, then on a sticker on the ram it will tell you the timing values. Eg :4-4-4-12.
Take note of these, look at the two 1gb memory sticks you intend to buy and make sure they Match the old sticks in speed and the timing values.
The board supports up to a total of four 1Gb memory sticks.
So two 512Mb sticks of memory size, and two 1Gb memory sticks will work.
You can mix and match RAM and your system will run. However it will be far from optimal. Ram speed will be slowed to the slowest stick in a group (if one is 333 and one is 400 both will run at 333). Timings will also be adjust for the lowest in the group (if one is 6-6-6-20 and one is 4-4-4-12 it will run at 6-6-6-20). Running different sizes will also disable some options like bank interleaving and dual channel.
Short answer: yes it will run but it will run at the slowest possible speed.