LiveCD's don't work

[Mike Fontenot <mlfasf@comcast.net>]

I just tried to boot from several liveCD's: both Knoppix and DSL. Both
initially start up OK (I get the two penguin images), but DSL hangs
before doing much else. DSL hangs after printing "Checking for for
USB...". Knoppix doesn't hang, but it leaves me in a shell that can't
seem to do much of anything (e.g., doesn't understand "init 0"). Knoppix
prints out this:

"Running Linux Kernel 2.6.19
Total mem avail...
Scanning for USB/Firewire devices...done.
Can't find Knoppix filesystem, Sorry.
Dropping you to a (very limited) shell.
Press reset button to quit."

I've tried two different CD's (a DVD in one case), and get the same
problem, so it's apparently not just a bad CD or DVD.

What's going on? Do I need to make some change in the BIOS beyond the
change I made to make the CD/DVD bootable before the hard drive?

I thought, since liveCD's don't modify the computer in any way (and
don't need any hard disk, only RAM), that nothing could go wrong.

(My PC is a Dell Inspiron 530).

	Mike Fontenot