When you burn the CD, you have to make sure to tell the program (Usually toast) to make the cd bootable. There should be a check box you have to click.
Or...you can look on the system cd and see if you can find a disk tools image. use disk copy to make a disk tools floppy, and this should support the cdrom drive.
If you have a non-apple cdrom drive, this will be a bit more tricky.
The of course there is the question why do you only have a burned copy of 8.1? Software piracy isn't a good thing...