It looks like you can use DDR OR DDR2 RAM, did you remove the 512MB DDR ram when you installed the 2 x 512MB DDR2 RAM? I could not find the QVL for the board's RAM, and you didn't tell us the make and model RAM you tried. It may work; it actually should work because almost all the DDR and DDR2 RAM meets the JEDEC standards - it was DDR3 that "escaped" to retail before the "standard" was finalized.
Since the board specs show it supports up to 2GB RAM (either DDR or DDR2), your BIOS shows only 1 x 512MB RAM, and there are no BIOS updates available on the support website, the only possibilities I can think of are:
-- The RAM/slot contacts are not making good contact; try wiping the RAM contacts with clean coffee filter paper, then install/remove/reinstall/remove/reinstall the RAM to clean the slot contacts.
-- The second stick of RAM is bad; try another stick.
-- The Board's RAM slot is not functioning properly; try removing the DDR2 RAM and installing the original 512 DDR, plus a new 512 DDR stick.
The orginal ram was 2 x 256ddr that's why I was trying to put in 2 x 512mb ddr2. I have tried what you said and I think the ddr2 ram slot in broken on the motherboard. Sometimes it will work with both chips in other times it will only boot with one in.
When it does boot with both in it thinks they are 256mb ddr 2 533 not 512mb.
Should I just put the orginal ddr back in and leave it.
I'm assuming it is the BIOS that is not seeing all the RAM. See if CPUz finds the correct RAM size in the operating system. If it does see all of it, then don't worry about what the BIOS sees.
Another thought: Have you installed the latest BIOS available for the board? BIOS updates are typically available on the the motherboard's support website, by going to the manufacturer's website, selecting the "Downloads" or "Support" tab, then using various methods, usually drop down menus, to find the motherboard BIOS updates, drivers, etc. Follow the instructions for flashing the BIOS - exactly as presented.