My own Asus A6T came with only one. Better brands come with one stick (at least ive seen several A6 series with one stick, both AMD as Intel). 2x 512MB is faster then 1x 1GB as it uses dualchannel. But 1x 1Gb gives more options to upgrade (cheaper). It is one of teh things ive looked at buying a laptop as i already did upgrade to 2GB (works perfect in Vista
). My Vista Mem rating got from 4.5(1GB) to an 5.4 (2GB duaclchannel).
To see wether your laptop has 1 or 2 modules without screwing teh backside open you should download this program. Fast and easy, check teh memory tab: