I recently bought a Western digital 250Gb media centre. Its quiet, fast and worked straight out of the box (just plugged it in [I've got XP home edition]). Personally, I think its worth paying the extra for the media centre to get the dual firewire /USB2 connectivity, the back-up software, and the additional USB2/Firewire/card reading ports.
It really is so simple. When you buy a caddie, it comes complete with its own internal cooling fan. Inside the box, which in my case, the £19.99 one, opened with knurled screws so that even a screwdriver was not needed, are the 2 connectors to plug into the Hard drive and these will only fit one way. You are supplied with the USB cable and the 13 amp plug, which drops the voltage, and mains cable. You need nothing else except the Hard Drive, which has to be NOT a SATA drive, and you can choose your own size and source.
I would beware of Western Digital, I used one of their USB drives for storage, after less than two years very light usage it failed. They don't do repairs/recovery, they don't stock parts, all they will do is refer you to a company who wants to charge £1000 for retrieval...if you use an 'unapproved' company that will void the warranty. Ironically it was used in part to backup the hard drive in my desktop computer which has had nearly four years heavy usage and is still going strong. This drive is manufactured by Seagate.