I have been running Vista and have had no problems with it. But then I ran XP PRO on my IBM Think Pad for years and it run great. My sister was a different story. But she has problems with everything. This is a Compaq I just bought 4 months ago and I ready like it except for the mouse/touch pad on it. The Think Pad was a better setup.
You can always buy now and install Windows 7 now or later, but remember that some of the drivers might not work for Windows 7. Google "drivers" if you don't understand the term. If you wait, you can buy a fresh computer with WIndows 7 and all the drivers already loaded and working fine.
So you can always check and see if the drivers are available for Windows 7 for whatever hardware the current computer that has Vista on it has. If the drivers are available for Windows 7 too, then you can just erase Vista and load up Windows 7 on it.