You need a motherboard that has the hardware, ACC support (SB710 or SB750 southbridge) or NCC and supports core unlocking, to unlock the extra cores on the CPU.
I wouldn't place any bets on unlocking cores on these cpus. I too have considered trying to save money / do up a cheap build and gamble on them. But the more I look into it the more and more leery I get. Even if you unlock 1 or even 2 cores odds are they will not be fully functional and/or stable for normal use or overclocking. Those cpus are listed as dual cores or triple cores for a reason, regardless of core unlocking ability. It really is a mixed bag. My advice is just buy a native quad core AMD and OC the bejesus out of it