So today I decided I was going to put Linux on my iMac so that I could have something more modern than OS-9 without having to pony up for OS-X (or more RAM to install it). This is a Sage iMac 450MHz with 128MB-RAM, slot-loader w/ DVD. Originally with 20GB hard-disk.
First thing was to take out the 20GB HD just in case I wanted to go back to OS-9, and because I wanted something a little bigger to start with. I had a spare 40GB HD laying around, so I exchanged that into the machine and got to reading.
It seems that Ubuntu dropped PowerPC support. YellowDog's mirrors were outdated - all except 1 or 2 that were hosted in the USA. The rest only had up through 3.x and I only found 2 with 4.1. So I downloaded those, as well as Ubuntu (as Debian itself has not dropped PowerPC, and I can always "swap" easily). Likewise, I also downloaded regular Debian.
YellowDog installed fine. I did a desktop install and everything was happy; however, it would not run X happily in anything larger than 640x desktop, and it would complain about me having not configured GNOME so it would go to an xterm.
Ubuntu complained and froze up trying to load, so I realized I had to go back and get the "alternate" CD because I have less than 192MB RAM.
Debian installed the fastest and easiest, but didn't come with any easy-X-configuring tools, and it seemed that default ATI didn't want to work with my iMac's ATI card. If all else fails I will probably go back to this and sit down for a few hours (ugh) and configure X properly.
Right now I am sitting at 60% of an install of Ubuntu's "alternate" CD ISO. If it works as Ubuntu has on all my other systems, I'm pretty sure I'll be happy, and when Ubuntu completely stops developing for PowerPC I'll switch my apt sources to Debian and ride their wave again.
Now having used the correct Ubuntu disk to install (my error) I have Ubuntu up and running happily on my little iMac. I definitely need to upgrade the RAM (in the mail already), and I'm not sure if once I get the RAM I'm going to be happier using Ubuntu (very familiar) which should be rather decent on a 450MHz/768RAM machine - or if I'm going to be happier using OS-X (not as familiar, but that's part of the fun) on this machine. I believe I'd have to run OS-X under "Classic" to get it to like this machine at all, and of course de-tune a lot of the looks of Aqua, but frankly I don't worry much about how my apps look - as long as they work.
The only complaint I have about the machine now is that Ubuntu does NOT like the iMac's integrated mic. I am not sure if perhaps my mic is just bad (I never tried it under OS 9 - so it may just be dead) or if this is something that I need to take one of those "a day of reading linux documentation to get it to work" kind of days on.