Well, If you want to buy a laptop now that lasts about 4-5 years, consider doing it NOW! ... The deals are here for Thanksgiving, and will be again for Christmas time at stores like, Best Buy and Circuit City ... Things you want to look for are The Express Upgrade to Windows Vista... (You should get AT LEAST Windows XP Media Center Edition now which = Windows Vista Home Premium Edition). You want a good processor, preferably an Intel Core 2 Duo or the AMD Counterpart, which i believe is the Turion64, and 1 - 2 GB of RAM, with at least 128 MB of Video RAM (for Vista). At the sale times you can get it for around $8-900 ...
Here would be a good example of one that is good now, and is quite expandable (in the RAM department) ... Hope this helps!