There doesn't seem to be any way of selecting a different system profile at boot-time with the default linuxconf shipped with RH6.0. Newer versions of linuxconf fix this, however.
Red Hat Linux doesn't use the "askrunlevel" utility of Linuxconf. You can manually enable this by putting the line: /sbin/askrunlevel as the last line in /etc/rc.sysinit. The Linuxconf RPM's from solucorp.qc.ca do this.