I will need to set up, with a very short lead time, around 20 PCs for use in a weekend-long tradeshow environment. These are just for doing mail, IRC, and IM. The boxes are Shuttles and come with no OS and no OS license.

I'm thinking the best approach here is to just stick one of the Linux Live CDs in each drive and let them go. Hopefully I won't have to do any configuring and custom ISO building. Really I just need something that will boot into an OS, get an IP address from DHCP, and provide easy access to a browser, Gaim, and an IRC client.

Anyone have experience with various "ready to run" Live CDs? Which one would be the best for what I need to do? Or is there another way (Windows is not an option and I'm not interested in Mac minis either, thanks).

Depending what you want to do with them, Knoppix should be sufficient.

All the applications you want are included in Knoppix.

Knoppix is the best known live cd and will do all of what you need. Version 3.7 runs well on my Thinkpad.

Just loaded Knoppix into virtual PC on my desktop, and yes; it does have Mozilla, Gaim and an IRC client.

There is also a SuSE 9.2 live cd... not sure of the differences, but if Knoppix doesn't cut it it might be worth a shot.

I'll toss in another recommendation for Knoppix. I keep a CD on hand at home at all times for emergency use (note to self, time to upgrade to the latest image). For what you want, it should easily do the job.

Knoppix is generally regarded as the stablest, most compatible, and most complete LiveCD system. It will work with just about anything.