BD (AM3+ as you said) isn't going to be backwards compat. It won't fit in either AM2+ or AM3. I think AMD stated AM3 chips will fit in AM3+, but the AM3+ won't work in an AM3 board.
I'd look to see if you can move up to a quad core CPU. If not, a PhII tri core would be a good idea.
Yeah, a PhII tri core might unlock into a quad, if you have a board that supports core unlocking