Hi and welcome to the forums.
If you are looking at digital DJ-ing, the laptop does become more important. Windows Vista is something that even Microsoft conseded was as big a failure going into Windows 7 as Windows Millenium was going into XP. Anything capable of running windows Vista should (theoretically) be capable of running Windows 7.
With software (true also for DJ software, especially with added FX, keylock or video modules for example) getting more and more demanding, there is something to be said for buying new or recent (up to 2-3 years old). Not only because of specs, but because of the dependability as well.
Hope that helps some.