Check out Debian. It has a good track record with PPC's, as far as I know
Yes. I run Debian on several Old World Macs with good success. One is a 5400 which shares the same motherboard as the U600 (the Alchemy mobo). Debian works much better on old Macs than YDL 3.0 and above does. I haven't tried Gentoo on PPC myself so I can't comment on that.
A vanilla U600 isn't really up to running the latest Linux desktop environments, but with plenty of RAM, a lighter window manager and sensibly-chosen apps it would make a serviceable desktop machine.
Alternatively, you could always put the machine to use as a server. I have a Starmax 3000 which acts the file and print server and network gateway for my local network. This is based on a derivative of the Alchemy mobo - the Tanzania - and it runs Debian well (and also has the benefit of being silent since I ripped out all the fans - it still never gets warm). In this case, however, I upgraded with a G3 card (they plug in the cache-RAM slot on the Alchemy, Tanzania and Gazelle boards - look for a Sonnet Crescendo or something similar). Memory is always going to be a problem, though - the Alchemy is limited to 136 MB, AFAICR.
You could probably run UAE on top of Debian. It won't be very fast though. I used to run Debian on my 604e. Never tried UAE on it though.
It'd be almost unuseable on a 166 MHz 603e. Look for a G3 upgrade card - or nag somebody to finish the PPC JIT. ;-)
Cheers,
Rich
