Hello people out there

I've been wanting to ditch windows for a long time but pressure of work has meant I haven't had time to look into it till now. This Knoppix idea looks really interesting: so I want to have a go. I've downloaded an ISO image, and written it to a CD, and followed all of the instructions I could find. I read the first ten pages or so of Knowing Knoppix. I put the CD in drive D, and rebooted the computer. I changed the boot options in my BIOS so that it looks first at the CD.

But knopix doesn't boot. The PC waits for a long time before deciding to offer me the option of re-installing windoes as a second o/s along with the windows I already have

What have I done wrong? Help!

Thanks.