VIA Edens are supported by an experimental kernel so I would hold on that for the moment.
For CPU a P3/Athlon 1Gig or higher should do nicely. I believe 128 MB RAM is the minimum, but as with most PCs, the more you have the better the experience.
I know nothing about the GeForce 256 so I cannot say.
My setup is a MSI nForce mobo, 1.8GHz Athlon XP, 1GB RAM, 40GB HDD, 48x CDRW, 32x CDRW/DVD, ATI All In Wonder, SB128 and 3COM NIC.
This works pretty well with AOS-XL and Amithlon, although under Amithlon I have to use VESA display modes.