"My Vista installation is getting very slow and probably has some errors on the C:\drive"
Run checkdisk for drive errors. If drive has errors, then not much point in putting a new OS on a dodgy drive.
If they are system errors and you want to install Windows 7 upgrade, no need to reinstall Vista.
Instead of doing an in place upgrade, boot with the Windows 7 dvd and select custom instalation, then select drive tools and format the drive using the Windows 7 tools. Windows 7 does the upgrade compliance check on bootup.
Don't forget to backup before you start.
My Vista installation is getting very slow and probably has some errors on the C:\drive. Should I re-do my Vista installation before upgrading to WIN7? Will a WIN7 "custom installation" re-format the drive? I hate to migrate to WIN7 on top of an "ailing" Vista install. Thanks for any advice.