Here is some info to get you started...
So, a motherboard that supports the AM3+ processor (125w) and windows 7. Check with the motherboard manufacturer for CPU and RAM compatibility.
At least 2 GB's of RAM (these days, 8 GB or more works best)
A power supply sufficient enough to support the 125 watt processor plus all of your other system components.
A GPU that supports DirectX 9 or higher.
20 GB's of hard drive space.