installing Debian linux from the internet to your Mac.
OpenBSD for 68k Macs tips
How To Load Debian Linux 2.1 Into An SE/30
Good Potato (2.2) Debian Linux install how to for the SE/30
Run Linux on your 68k (Non Power) Mac - 68020 or up). I did this myself, and while it's not easy for us Mac users to learn a command line interface, it's kinda fun once you get X (Mac type interface) to work. I use my SE/30.
Linux m68k site - everyting you ever wanted to know about Linux for m68k computers.
Learn Debian GNU/Linux online book
Good overview of the various Mac Linunx distros
Networking your Mac to a Linux box with a null modem cable.
Linux mailing list for 68k Macs - Mac II, SE/30, etc.. very cool
More 68k Mac Linux mailing lists
Debian Linux has been ported to the Mac SE/30. It WON'T work on the SE as previously reported by others and repeated here.
Great Mac 68k Linux page

Mac OS Emulators for Linux

http://www.ibrium.se/linux/mac_on_linux.html
http://www.ix.de/ix/artikel/E/9611064/artikel.shtml
http://MaceHQ.cjb.net/
http://www.vmac.org/
http://www.uni-mainz.de/~bauec002/BAMain.html
http://www.uni-mainz.de/~bauec002/B2Main.html

Sites for text browsers and slow Macs
Info on Apple's version of Unix - A/UX (no longer made or supported by Apple)
MachTen is a Unix distribution that runs NATIVELY (no need for an extra drive partition) on 68k and PPC Macs. I'm running it on my iMac and Centris 660AV. Includes AfterStep, a NextStep GUI clone.
Attempting to learn Debian Linux on a Mac SE/30 ? Here's the book for you.SheepShaver lets you run MacOS under Linux.
MacOnLinux is another MacOS 'emulator', but not really... check it out.
BeOS - cool OS from former Apple employees
MKLinux mailing list - PowerMacs
More MKLinux lists
Linux PPC mailing list- for Linux on PowerMacs
MAX is Low End Macs Linux email digest - free.
Simple Unix cheat sheet for Linux on Macs.
MacBochs allows you to run Linux, FreeDOS and other OS's on a 68k or PowerMac (NOT 68000 Macs). The cool advantage of Mac Bochs is that you can download pre-installed operating systems on disc images that decompress to 200 meg drives or larger. You can also install new packages (system software parts) to these hard drives. HIGHLY RECOMMENDED. Works on my iMac too.
Unix Novice Guide
Run Unix on a Mac Plus while booted off a floppy.
Linux on a 68k (Non PowerMac)
Added more info to the MacMinix page- (it's now free!) and run it on your Plus or up, System 6 or up. No need to reformat your hard drive.
Mac06 - Run a Unix-like interface on 68k and PowerMacs without reforamtting your drive. This is a limited demo, but it's cool.