First of all, wrong forum category.
In one word:
no.
It's A LOT more difficult than you might think. You can't simply "plug it in" to a DC converter like somebody above me suggested. If you don't have an aftermarket headunit, you're going to have to buy a line-out converter and wire your powered-sub in line with your rear speakers... if you decide to get a separate amp, I have no idea what the impendance is on a Klipsch computer sub, but I don't imagine you squeezing a whole lotta bass out've it... let alone figuring out how to wire it.
Bottom line: Klipsch speakers are best kept where they belong -- on your computer desk.
I'm not quite sure why anybody would ever WANT to do this, since the 2.1 THX Klipsch system runs for about $150... You could get a decent car audio sub for that price and it would sound a helluva lot better. Why spend $150 on something that has no place in the car....?