I dont have any micro itx boards myself, but have used aros on a lot of different hardware over the last 7 or so years. These days it works on more hardware than not (although with varying degrees of support). In regards to mobos most socket 775 core logic chipsets work (945/965/p31/p33/p41(and others Im sure, but Ive not used others)) and at least some am2/am2+/am3 based boards will work (although Id be surprised if there's many micro itx boards based around amd cpus (too hot/power consuming). In regards to socket1156/1366 Im not too familiar with small form factors so I cant really advise here. Graphics wise, most cards at least have vesa working (aros vesa drivers are quite reasonable), but for hardware accelerated graphics you'll need to use nvidia from tnt through to geforce 6 for the original aros nvidia driver or for aros nouveau drivers gf1 through to gtx295, but bare in mind 3d acceleration (full gl2.x so far as I know(possibly 3.x on appropriate h/w, but I dont think so)) is only supported from geforce5 through to nv50 (gf8/9 based gpus). Additionally there's also 2d accelerated drivers for both intel and amd/ati gfx (although only up to x850 so far as I know for amd/ati). As for nic drivers I've only ever used rtl8029, intel pro 100 and a 3com card, but I know there's other options, including some onboard nics (rtl 8111/8169 maybe?). Additionally there's also now alpha wifi drivers, but I cant really elaborate as Ive no wireless gear so havent tried them. Sound wise there's HD Audio drivers, which are probably pretty common for micro itx boards.
