Macbook Pro wont start up

I have a Macbook Pro with OSX 10.5 installed on it. Long story short I set up the mac to boot using the cd drive, restarted it and now it wont boot with the cd. How do I get my Macbook Pro to boot using the harddisk instead of the cd drive? I have looked at a couple of sites and they said to hold down shift to go into safemode, and to hold down "D" to force it to boot with the hard disk but neither of those worked. If I turn it off and on it still trys to boot with the CD drive. My mac was working perfectly and hour ago and now it wont start up...please help.

I seem to remember that holding "X" while booting forces a startup in OS X. Try that.