Root Permissions

Hey all,

Anybody know of a way to execute a command as root by supplying a password?

--OR--

Anybody know how to write to a root write permission only file without
changing the
permissions of the file, while not allowing any other scripts to alter it?


-----
What I'm trying to do - Alter the Sendmail virtual user table file
"/etc/mail/virtusertable" for administration
purposes using the same webserver as other people whom I do not "trust" (in
the security sense of the word).
Plus - I need to restart sendmail when I'm through "/etc/init.d/sendmail
restart"?

Help,

Dave