What is the best live CD linux out there?
I have Knoppix now but is based on debian and it is different from my previous version of redhat 9. Is there some live CD linux that works with rpm's?
Under Knoppix i couldn't login as root, it was very confusing and i was unable to install any software, is there an live CD version of linux that doesn't have this kind "problems"?

You can't install programs, at least not in an easy way, with a LiveCD. Just think, where will a new program be installed? You've to install it on the hard-drive to not get those "problems" as you mentioned. Go to:

http://www.linuxiso.org/

make a search after LiveCD. There're a bunch of those around... but if you want to be able to install programs, create accounts and have better performance, you've to make an hd-install. Actually, the best is to get a full, good distro and install it to the hd. Live distros are good as a repair disk and to show your friend that Linux really works. Or to test a computer before buying one... other than that, pick up an ordinary distribution

Check out www.distrowatch.com for live CD versions.

Did you install to hard drive or just running from CD? If running from CD then you can't install apps like you would with a regular distro. Basically your / is a ram disk.

http://www.knoppix.net/docs/
There is no root password; all passwords are locked by default. You can set it by going Knoppix Menu->Root Shell and typing "passwd", then enterting a root password, also there are several sections you can read dealing with this subject in KNOPPIX/README_Security.txt. You can also type "sudo su" or "sudo -s" in any console window, or use <ctr>-<alt>-F2 to get at the text console with already opened root shell.