FX 4100 (and all the other bulldozer CPUs) dont really have as much power as the core-count would make you think. They appear to have 4/6/8cores, but is due to the way that the 'cores' are counted. They dont have 4/6/8 'full cores. Normal 'cores' have seperate instruction fetch, decode, integer sheduler and interger parts. The bulldozer 'modules', which are counted as 2 'cores' have shared instruction fetch and decode parts. Its more like 1.5 cores per module, not 2 cores.
That said, there isnt a huge difference between a X4 965 adn FX4100. I'd probably get a X4 965 myself.
As for a motherboard, Id get an AMD 9XX chipset board. All the major motherboard manufacturers make them (well, apart from intel). If you dont need crossfire/SLI (you wont unless you are a gamer) AMD 970 chipsets are cheaper, and will work just as well as the more expensive 990X/990FX chipsets. BTW, you could get an AMD 8XX chipset board for the X4 965, or Fx4100, but I would suggest its worth getting a970 chipset board, even if it costs a little more.
*Edit- you might find the post I made here worth looking at-
http://www.linuxquestions.org/questi...ml#post4571842
