It will fit in AM2/AM2+ socket provided you mobo manufacturer released a BIOS update for AM3 cpus. http://en.wikipedia.org/wiki/Socket_AM3
If you have a branded pc like from Dell or HP,there are fewer chances of finding a BIOS update (OEM boards are designed with almost no consumer end tinkering in mind). If you've assembled the pc yourself then there is a good chance a BIOS update exists.