sadly the data in a DVD or CD burned at high speed will likely be decently ok as such,
BUT the data may be in some of the backup sectors which are not that accessible to a operating system that is trying to start (still just basic hardware support)
also a MD5 check will prevent making coasters (bad burns) in most cases, specially if disk is then burned at low speed.

you can find much usefull information on the WIKI.
http://www.knoppix.net/wiki/Main_Page

read through this FAQ for information on Burning and MD5 among other topics.
http://www.knoppix.net/wiki/Downloading_FAQ
I strongly advise reading most of the FAQ, it may answer some more Questions you did not even know you should have asked.

I think the sections you are interested in are mainly the ones below (guess I make this too easy for you)
http://www.knoppix.net/wiki/Download...O_CD_images.3F
and
http://www.knoppix.net/wiki/Download..._using_NERO.3F