Mac OS X installation discs that came with a PowerPC processor-based Mac won't work with an Intel processor-based Mac, and vice-versa, even if both Macs came with the same version of Mac OS X. You can't start up an Intel-based Mac from a CD or DVD that came with a PowerPC-based Mac, nor a PowerPC-based Mac from an Intel-based Mac's discs, either by holding the C key at startup or by using Startup Disk preferences.
To start your computer from a disc, use the disc that came with the computer.