Changing users in php script

I know php runs under the same user/group as the webserver for web based applications, but is there a way to change to another user? All the recent talk about exec got me thinking that I could set something up to automatically create user mailboxes under qmail + vmailmgr. I normall do this via the command line by running 'vadduser' while I'm su'ed to the owner of the virtual host. So basically, to do this via php, I would need to su to the owner of the vhost inside of the script, run the command, and exit out of the su. Can this be done? -- By-Tor.com It's all about the Rush http://www.by-tor.com