Building own computer for the first time, few questions

First, any blaring mistakes in this build?

Case: NZXT BETA EVO Classic Series CS-NT-BETA-EVO Black Steel http://www.newegg.com/Product/Prod [...] 6811146059
Mobo: GIGABYTE GA-MA770T-UD3P AM3 AMD 770 ATX AMD http://www.newegg.com/Product/Prod [...] 6813128392
PSU: SeaSonic M12II 500 Bronze 500W ATX12V V2.2 / EPS12V 2.92 80 PLUS BRONZE Certified Modular Active PFC Power Supply http://www.newegg.com/Product/Prod [...] 6817151081
Ram: 4GB (2 x 2GB) 240-Pin DDR3 http://www.newegg.com/Product/Prod [...] 6820227495
CPU: AMD Phenom II X3 720 2.8GHz 3 x 512KB L2 Cache 6MB L3 Cache Socket AM3 95W Triple-Core Black Processor http://www.newegg.com/Product/Prod [...] 6819103649
Graphics Card: SAPPHIRE Radeon HD 5770 http://www.newegg.com/Product/Prod [...] -_-Product

Then I'll be using a hard drive and optical drive from my old computer.

And one question, if I'm using my old hard drive will I have to reinstall windows?

Well i dont see any problems with the rig, you can never keep up to date fully with computers. There is always better but you will
pay an arm and a leg for it and then it will be out dated in a month. But all in all for the price it will be a good Rig.

As for having to reinstall windows, as long as you uninstall all drivers for your MOBO, Video Card, Sound Card, and any other
component that you had hooked to your old computer you should be good to go. Just make sure to uninstall them befor
you put the harddrive in your new Rig.

What i would suggest is to install your harddrive and hope that it will let you in to back up the things you want.
If you can get them off there, then i would do a format and do a clean install of windows. Most of the time you can
put your old harddrive in a new computer and still get to windows but with complacations, the system will never run right
after that unless you format.