You won't have to reinstall, but things will work better with a fresh install of Win 7 over an upgrade to Win 7.
This is excellent advice. Upgrading weirds operating systems.
I actually just nuked my old Vista system from orbit yesterday, re-partitioned the drive, and installed Win 7. Working great (knock on wood). Of course, I subsist on very few apps (Firefox, Thunderbird, OpenOffice, Gimp and STO), so re-installing was not such a hassle.
if you upgrade from vista home to 7 professional (or ultimate, i think) you have to do a clean install. i went from vista 64 home to 7 64 professional and i had to do a clean install and call microsoft to activate it.
although Win7 gives you the option to install while keeping your Vista files, I highly recommend doing a fresh/complete install rather than upgrading. There always seems to be weird, annoying, and sometimes troublesome issues that pop up with upgrading.