Check for the little hole that should be on the right side of the CD drive. You should be able to use a straightened paperclip and push it in the hole to open the drive.
Now you can put a bootable CD in (OS CD preferably) and then holding down the C key to boot by the CD after you power it up.
OR, you can try starting it and hold down the C key. It will say no CD in drive and open the tray (I think).