I work for Best Buy as a Geek Squad Supervisor. The way it works is you get comprable technology up to the price of the original notebook. If you bought the prior notebook because it was a 14" screen and thats what you want, so long as it doesn’t go over the original price your fine. Again I say "comprable" because you cant exchange a PC for a MAC.
The first thing to know is this. We are unable to fix the ASUS brand computers. If manufacture parts go out within the first year we will just end up replacing it (until our contract changes, which it probably wont till 2010). The rest of the brands we carry we would have to follow manufacture policy and send it to an authorized repair center. Because I service them on a daily basis my recommendation would be to stick with HP or Sony.
The second part is that all the new computers that we have only have Vista SP1. The manufactures refuse to put on SP2 before the launch of Windows 7. None of the computers except for Dells come with restore disc, so keep that in mind. You will be talked to about optimizing the computer for $39. If you have no experience with computers I would just go ahead and have the Geek Squad there create the Restore discs and do the optimization. I say this because Microsoft recently put out updates that blue screen computers if they don’t have Vista SP2. If you bring it back 2 weeks later your SOL because the service plan nor manufacture will cover it.
Thats about it let me know if you have any questions. For some reasons some Best Buy stores will bully customers into certain models because they are trying to protect their margin.