Oh, yes. To get into Open Firmware, reboot your Mac while holding Command+Option+O+F
Make sure it is typed CORRECTLY making sure you're using capitals wherever I have capitals in this code. It is important!
dev /cpus/PowerPC,G4@0
d# 867000000 encode-int " clock-frequency" property
d# 867000000 encode-int " min-clock-frequency" property
d# 867000000 encode-int " max-clock-frequency" property
boot cd,:\\:tbxi
The last portion of code is very important to include. Be sure your Leopard DVD is inserted before you hit enter after you type "boot cd,:\\:tbxi"
It was a long stressful night for me, but it worked. Here's how it turned out:

If it doesn't work. Tell me through PM, or post it here. Mods please sticky!