Second Hard Drive.

[Kotto*N[ix]mouth]

I'm guessing that since you're used to Mint and Ubuntu, Arch and Slackware may be to far for you right now. Then again, I don't know how much you know with CLI, so who knows.
Since it'll be on your desktop, I would actually suggest trying Arch. Below are some useful guides that would help you install it. These are somewhat old, since he installs GNOME 2 and not 3. But, you could go to the Arch Wiki and find a guide for whatever desktop environment you wish to use.
Part One:
[yt]http://www.youtube.com/watch?v=RjTTl_9aUXc[/yt]

Part Two:
[yt]http://www.youtube.com/watch?v=azySq-uBaB8[/yt]

Part Three:
[yt]http://www.youtube.com/watch?v=2xF60AQu-K4[/yt]