In order for kppp to run correctly as a user other than root, it needs to be setuid root. I don't know of any security problems with doing this-- doing a 'make install' from source makes it setuid root, and it's also that way in the official KDE packages for RH52.
KPPP has not been through a security audit. We do not ship SUID non-security audited programs. You may set it SUID at your own risk.