Hydro: AMD, the company, bought up ATI which used to be a separate company. This does not mean that you need an AMD processor or an AMD chipset to run a ATI video card.
You asked about 32- vs 64-bit "OC", which I'm guessing is supposed to be OS, "Operating System". A 64-bit OS is not going to be a resource hog by comparison to a 32-bit OS. More resources, yes, but not a *lot* more. Some advantages of 64-bit Vista is that you can access all 4 GB of that memory you picked out and more. Vista 32-bit can only access about 3.2 GB tops. A 64-bit OS moves more data and can operate on more of the data, thereby increasing performance. Vista x64 will be less compatible with games, especially any that are older than 2 years.
The external drive dock, the Thermaltake BlackX, is intended for people who have a lot of drives lying around and need to swap them out frequently. It might be cooler, depending on the ambient temperature and air-flow in the room where it's kept. It will almost certainly be noisier than an enclosure which would provide some acoustic dampening.
The Samsung Spinpoint drives are well regarded, as are Western Digital Raptors (for speed), and Seagate Barracudas (for reliability). Mixed reviews are not surprising because there are so many trade-offs to make in a hard disk: speed, reliability, acoustics, power consumption, density, and so on.