2x256 or 1x512 MEM?

Should I get 1 stick of 512Mb DDR or 2 sticks of 256Mb DDR mem? Is ther any speed difference?

There shouldn't be any speed difference - I would look more at the cost, and the space. A 512MB stick will leave more slots free for later expansion, whereas 2x 256MB will use up more slots.

Also, if a 512MB stick is cheaper than two 256s then go for the 512.