Find a 3.5" hard drive enclosure. They can be had for $20... Then you can
choose whichever brand harddrive that you prefer.
They can be moved between PC's. They do need to be formatted in a compatible
format though. Formatting a drive in Windows XP means you won't be able to
access it on a Windows 98 machine, for example.
Noozer is right, bgm.
Get a firewire\USB case with it`s own PSU and stick in a good
big HD of your choice (it`s easy, 4 screws and the 2 cables)
And format in Fat32 for best compatibily across machines.
I use an `ICYBOX`, it`s got no cooling fans, but it`s like
picking up an ice cube.
I feel there`s no need to keep it running all the time.
After all it`s only used for backup\safe storage.