In my two cents...
IF all the hardware is brand new, and states it supports Vista then you are safe!
However, if you have an old inkjet printer, or old Virus software like Norton Anti virus 4.0 to 6.0, even Nero software 6.x or before it will not work on Vista!
Give you an example to clear the matter up. I sold a system to a customer yesterday who only uses her machine for word, outlook and internet. She doesn't need music or anything fancy. Her printer is a Lexmark Z715 which isn't supportive for Vista, only XP. So, she has to buy a new printer. The Norton she has is 4.0, so she had to choose from a different version.
And the Nero software for Lightscribe is only 6.0 she needs 7.x at least to be supportive.
So, if all the components are NEW... no problem. Once you try to add some old device you will run into a problem. Fortunately some HP printers will work just fine in Vista.
So, it is faster as to accessing data and programs, and the Aero is awesome to see too.
Hopefully you can use this rule of thumb to make a decision.