it's probably the permissions or the suid bit on the ppp program - just as a quick dirty fix, you could run
chmod +s pppd
in the /usr/sbin directory (i think...
) - there might be another script or two that you would need to do the same thing to - depends on the implementation redhat uses - unfortunately, i'm not too familiar with it.
anyway, what that does is set a bit in the file attributes so that the file will execute with root permissions regardless of who executes the program. for a desktop system, this isn't a real security risk, but it's not something you would want to do on a larger server system. if you want to take the trouble to get it working the correct way, then you need to set your use to a group allowed to use the scripts - which is quite a bit more work.