To elaborate on what he said:
SATAII is backwards compatible. This means that a SATAII HD will work on a mobo that doesnt support SATAII. SATA HDs will also work on SATAII interfaces.
Nowadays, SATAII is pretty comparable in price to SATA, so if it comes down to it, you might as well get SATAII. If you can't manage to get a SATAII HD, or it is more expensive, don't even bother with it, as the performance difference is nearly non-existant.