Assuming the CD is bootable
The way that *always* works (when the C key thing doesn't) is
<Shift>-<Cmd>-<Option>-<Del>
Not as intuitive, but usually works on older Macs (say, from the Power Computing days).
Another way, if you can boot to your hard drive and are running OS 9 or better, is to use the Startup Disk control panel.
Of course, I'm also assuming you're not being sarcastic....