Well, since pppsetup is not in the users path you could call it with the full path:
/usr/sbin/pppsetup. However, the first thing pppsetup does is find out if you are 'root' an di fnot it will warn you and quit.
to runn commands as root without having to logout and back in use 'sudo'
just type 'sudo /usr/sbin/pppsetup'
However, you'll find that pppsetup will not give permission for users to dial out. You'll have to chmod some files after running pppsetup.
chmod 6755 /usr/sbin/ppp-on, ppp-go, ppp-off, ppp-stop, and pppd
Then chmod 644 /etc/ppp/options and /etc/ppp/pppscript
and chmod 600 /etc/ppp/pap-secrets or (chap-secrets)
This should let users dial out without sudo-ing.