I'm don't know much about AMD but I know this, get a crossfire motherboard. Here there reason, ATI is part of AMD family. So is natural that the get better board for there ATI card and less care for a Nvidia chipset. Also the AM2 CPU will work on a AM2+ socket.

I would recommend getting an AM2+
the phenom might not be as good as an intel CPU... but that's only if your doing video editing .. or rendering ...
if you just playing games.. or just use it for everyday use.. it makes little to no difference... in fact most cases going the AMD route makes more sense cause they are cheaper than their intel counterpart ( getting more for less money )
also the most common problem with AMD isn't that they are bad... is that they cant make their cpus reach speeds beyond the 3ghz at std factory settings... or able to overclock well... ( intel duo core overclocks really well ) .. if you don't want to overclock and just put one AMD and one intel CPU at stock speeds in comparison ... the difference is minimal ( specially in games )
also this problem with overclocking an AMD CPU to higher speeds will be resolved once AMD starts making 45nm Phenoms ..and the first ones of those will be AM2+

the only question remains ..which is more up you.. is which AM2+ chipset are you thinking of getting ?
which translates to:  how much money you willing to spend and what is your primary use of your computer on a day to day basis ?