qhn's formula looks about right.
what are you looking to use it for? inside and/or outside? not all tablet screens are outdoor viewable. how long of a battery life do you need? i can squeak about 3.25 hours out of my motion le1600, others do better, but some take a long freakin' time to recharge. what kind of resolution do you want? are you concerned w/ performance? i.e., are you looking for a core2 duo? do you want a detachable keyboard? do you want a 10" or 12" screen?
give more info and we can give more help. fujitsu is not flat out the best, but it probably does some things better than others.
check out these forums, which specifically cater to tabletswww.gottabemobile.comwww.tabletpcbuzz.com