I use a utility called GameMode
http://download.cnet.com/GameMode/3000- ... 07864.html
One click and it shuts down all uneccessary running applications,services and procedures. Note I said it shuts down any open apps too so you run this utility before starting your karaoke application(s)
Then click again to restore back to the way it was.
I actually just close the GameMode app too once it is done doing its thing and just restart my computer to restore all.
There is also another app like this one called GameBooster
http://www.iobit.com/gamebooster.html
Both are freeware.