Well for starters you really don't want to run it through a home theater system, the speakers aren't really designed for live vocals. You may be better off buying an all in one unit. Maybe something like
http://www.karaoke.com/cgi-bin/WebObjec ... key=350268
Not sure what your budget is, but this comes with a couple wireless mics, 1500 songs to get you going, plays several different types of media & is on sale right now for almost half off. This is a self contained unit basically plug in & go.
You can set up your laptop to be a karaoke player, but then you run into needing to buy & convert your discs that you buy - there are a couple of legal download sites that you can buy each song. And again, you'd need to run it into your home theater, which isn't recommened as you can blow your speakers.
Other opinions are sure to follow - this is just 1!