I'm playing around with a borrowed Samsung X10-1400 from Dixons. Its a nice machine but doesn't get near the 4.5 hours as Samsung have put in a smaller battery to keep the weight/size down - I only get around 1.5-2 hours out of it.
The Toshiba Pro M10 is a much better system for battery life, you will get over 4 hours on that. It costs around £1599 and has an average spec in terms of memory, graphics and hard drive but it sounds like you don't need much. The Pentium M 1.4Ghz processor is more than sufficient - it beats a P4 up to 2.4Ghz when run off battery and handles games fine too.