The 5600+ will work in any AM2/AM2+ mobo. That wont be a problem. The problem will be getting a AM2+ mobo. At my work we don't have many left. In fact we only have one. Most are AM3 mobos.
Honestly I would save the $50 and save up for a new setup. The 5600+ wont give you enough of a boost to justify it. Only a completley new system would. Even you going to a Llano system, the A8 series of CPUs, would be worth it and they are pretty cheap.