Problem
You want to allow a user to run one command, as root user.
Solution
To allow a user access to run stuff as root, just login as root and then add the following line to /etc/sudoers.
userid hostname=command
Example
For example to allow user marcus access on bree, to restart, stop, start or check apache:
marcus bree=/etc/init.d/httpd
To allow all access on all boxes:
marcus (ALL)=(ALL)
Reference
[tags]sudo, switch user do, temporary UNIX authorisation, Unix Coding School[/tags]