The Athlon 64 is OK. There really aren't any "bad" choices among the latest CPU's, the way there was with the Celeron vs. Pentium years ago. There are better choices in terms of power:performance (ie, watts of electricity and heat vs. speed) to be seen in the latest Intel offerings -- the Core product line produces lots of performance at lower power consumption, but there's absolutely nothing wrong with the AMD/Athlon product line.

To see barebones systems, go to TigerDirect, NewEgg, et al and have a look. There are literally dozens of barebones systems out there, in all manner of CPU/mobo configuration, some with memory, some without, etc.