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