To boot from a Solaris CD -
First take the machine down to it's OK prompt, use init 0 or Stop+A or if all else fails pull the keyboard cable out and then put it back in.
Then boot it from the CD
OK boot cdrom (use this to start the Solaris Installer) or
OK boot cdrom -s (this will boot the machine from the OS image on the disk)
I'm have never used Redhat, but it must be similar.
Steve