A tutorial for booting off a live CD would be rather short. Download, burn CD and reboot the computer with the CD in the drive is all that is needed in most cases.
In case you are having problems to get it to boot correctly there are a few steps you should check.
1. Check if your hardware is fully supported if some additional drivers/steps to get everything working
(This is a good place to start http://backtrack.offensive-security...._Compatibility)
2. Confirm the checksum of the downloaded file(s)
3. Re-burn the CD at a lower speed (1-2x)
If you still are having problems after this post your hardware information along with the error messages here and someone will surely be able to help you out.