How do I know if certain parts will work in my computer?

[CBJ023]

Yea, I was ready to buy everything but I'm defiantly going to switch to their $255 bundle and throw in a ASUS Radeon 7770 Once their sales rep. gets back to me I don't know it it'll need a new power supply to support the new graphics card but for me it'll end up costing cheaper, have better parts, and a better case