I had been using a 3ware 7500-4 for 2 years before upgrading to my new opteron. (read other post about chipset compatability)

I was using an old Intel 440bx chipset board, with the thing in 32bit/33mhz slot. No problems.

Yes.. there are 33mhz/64bit slots out there, in some of the first gen 64bit boards (alpha cpu boards come to mind)

I was previously running 2.4.x with my 3ware, no problems.. and 2.6.x also work fine. I would reccomend 2.6.x, it's been very nice on my new server. (having alsa and lm-sensors in the main kernel is very nice)