I upgraded to Vegas 7 from v. 4 some time ago. Vegas 4 is still on the hd and not used since. I want to remove it completely but will uninstalling cripple my Vegas 7 which works fine?
They usually exist as completely separate apps, so uninstalling 4 should not affect 7.
You can always install 7 again if something goes wrong? Have you registered 7? If so, this website has the serial numbers of all your Sony software under the My Account>My Software section.
It's very easy to reinstall if you need to. Don't do it in the middle of a project. Do it when you have some downtime.