If you had the choice between the two, with almost identical specs:
Processor: Intel® Core™ 2 Duo processor T5600 (1.83GHz, 2MB L2, 667MHz FSB)
Windows Vista (Home Premium on Sentia, Biz on Thinkpad)
2 GB memory
100 GB 5400 rpm hd
WXGA 14" screens
6 cell batteries (can't get a bigger battery than a 6 on the sentia)
What would you choose? Alienware is $250 cheaper all in even after Lenovo's St. Paddy's day sale.