IIRC the C3 is clocked at 800MHz?
There are a number of variants up to 1GHz, but the 1GHz is very hard to find.
It does come without a heatsink though, which means you can fit an oversized
heatsink for passive cooling. The EPIA series chips are fully integrated with
the motherboard - they are soldered to the motherboard and the small heatsink
is not designed to be removed.
That means the higher speed integrated units such as the M9000 will be hard to
make completely silent unless you want to risk prising off the original
heatsink.
As for power
supply transplants, I'm sure it could be done - you could
even put the rackmount PSU in the Procase to avoid wasting it...
I'm not sure there the same shape, the 1U supply is long and thin.
There's lot's of case-modding ingenuity described at
http://www.mini-itx.com
though.
Via's documentation for specific Linux distros is at:
http://www.viaarena.com/?PageID=60
Interesting to see that they list Red Flag ahead of Red Hat...
Cheers
Daniel