lol im very new and don't know so much but i'll tell you what i've learnt.:happy:
Ok seems your board can take 2GB of ram so yeah you can do 512mb or more fine.
the difference between DDR and DDR2 is that DDR2 is like the next generation of ram up from DDR, basically it's twice as fast( is that correct) and is the RAM and is generally used in most computers today.
Prices for DDR ram varies ALOT, for example one site has 1gb sticks at the insane price of $150...
this is the correct ram, your probably not going to find it much cheaper and Samsung is a name brand.
Interesting that on that site 256mb and 512mb cost the same, lol.