you can also if you wish make one virtual disk out of two harddisks, gaining a bit of speed by constantly writing on both harddisks (as an example think of a word document that when you save it saves half of the page to harddisk one and half of the page to harddisk two, both harddisks can write at the same time, which makes it twice as fast in theory.
That's what i'm doing. Then i compressit over night using....
oh yes....
::drumrolls::
DriveSpace 3! Whohoo!