Im pretty well versed in amithlon, have used it on a variety of hardware over the years.
Hardware support wise:
sblive, sb128 or some ac97 based sound is probably the most common stuff. For gfx card, matrox (up to g400/g450) cards have full hardware acceleration. Nvidia from things like tnt through to gf4 ti based cards (I think gf4 mx cards though can be problematic), plus a handful of gf5 based cards. Gf5200 has ful support, as do 5500 and 59x0, I think I few others as well, but Id steer clear of anything Ive not listed just in case. Ati support is limited, and only partial acceleration is available to some cards. Because of this Ive not really tried many ati cards so I cant really tell you anymore there.
Network card wise most cards that are ne2k compatible should work, but to be safe maybe stick to a realtek rtl8029 card, or maybe an older 3com card. I believe there's some nf2/3 based nics that are supported too, but Ive always just used one of the above.
As for mobo support, over the years I started on an athlonxp, from there to an athlon64, and then to a core2duo machine, all of which have worked nicely. The most recent architecture I have experience in amithlon with is a core2duo/socket775/g31 chipset based machine. I believe up to g41 based boards are supported (I think ich7/8 and 9 are supported with latest kernel).
Despite having used, and very much liked amithlon for a long time, I was pretty surprised at how much of a speedup I got going from an athlon64 to a core2duo based system. It really is usable for most typical uses of a computer these days. Movies run nicely, 68k uae run even aga software full speed/full framerate, mame is good, quake 2 gives me 100ish fps, etc, etc.). Even 68k OWB is surprisingly usable (once pages are fully loaded at least).
Anyway, feel free to ask if you have any more questions, it's probably fairly reasonable to say Im one of the more experienced amithlon users still around so should be able to help when/if you need it.