Late 2006 iMac without OS: How do I boot to reinstall?
If you Tiger DVD is not bootable it might as well be PowerPC one.

If your iMac is Late 2006 it will support Mac OS X 10.7 as latest.
You can buy it from Apple for 20$. System requirements for OS X 10.7 is at least 2GB RAM though. So you might check first if you have enough. These are guides on how to get to the memory.

Then you will need USB pen drive and Lion Disk Maker to make it bootable out of bought file.

The mac will accept 2 or 3GB of DDR2-667 SODIMM RAM total(depending on exact model).