CDR is easy enough. Its all about which options you select. I wont cover actually getting the distro that will boot from CDR, since there are so many.
The trick is that when you are burning the CDR you need to select "El Torito" bootable CD. (El Torito is for x86, you need others depending on what arch you use). You then need to point to the location of the boot image.
I'm not sure which burning software you use, but I recomend X-CD-Roast (www.xcdroast.org
). This result is easy to acheive in X-CD-Roast, when on the "Master Tracks" stage of production, select the "Boot Options" tab. Then tick the right boxes etc etc, its all fairly simple.
I'm not sure what you mean by a bootable CDR, if you mean a live distro I strongly recommend you try Knoppix (www.knoppix.org
Hope that was of some help to you.