Boot from the Win7 DVD and choose Custom install>Advanced drive tools to format before install.
If you have an Upgrade, it will scan the HD and see Vista to allow Upgrade key.
The Win7 DVD is nearly driver-complete, with newer ones added during install if you first check the box to "Connect to the internet during install" and keep ethernet plugged. Afterwards Windows Updates will have a few newer ones. Any rare drivers along with some apps can be found on the Support Downloads page for your model computer.
If you want to make sure you have all of the drivers to migrate from Vista, back up windows/system32/drivers and /driverstore files, later browse to it from Device manager for any missing drivers after Win7 install.