IndyColtsFan
Lifer
Also I'd suggest jsut getting the 250GB model now.
I agree with this advice. Unless you have another Xbox hard drive handy, it is probably better to just spend the extra $100 and get the model with the 250 GB hard drive.
OP, as others have pointed out, you can't just buy any laptop drive and place it in the Xbox (you can on the PS3, however). What you can do is buy a used Xbox hard drive and then place it in the Xbox Slim Arcade, but honestly, I don't think it is worth the risk of getting a bad drive.