Probably a bad idea using that tower... A new tower will come with all the wires labelled, a new power supply, and enough screws hopefully +)
Buy a new tower, they come in all flavors for less that $100 or a good one for up to $200+.
Building a system is quite simple, just read the manuals, and take a look at something thats already assembled if you have one, just to get an idea.
Another possibility is buying a custom rig from a small local store. When I say custom, YOU choose the components, they assemble it.
We can coach ya as far as what to purchase.
SKurj