Vista is differs a great deal from Windows XP.
Personally, I agree with your parents. XP is not only familiar, but it is compatible with more software then Vista.
XP is more compatible with 3rd party appliances like printers and scanners.
Though the above will change as Vista grows older,...
Vista is a resource hog. Vista requires your computer to have over 1 GB of RAM so that it can do its fancy Aero 3d thing that isn't useful.
Vista is a major change from XP, although I doubt that would be a problem to you.
Finally, if your parents already bought XP, why force them to spend anywhere from 1/4 to 1/2 a grand on a new operating system?
As of now, Vista is probably not the right choice for your laptop. Besides, Microsoft has already announced a new operating system that is 'better' then Vista. Windows 7.