There are a number of wireless/remote comtrols that you can add to your PC that will let you do almost all of what you want. I use two different remotes on multimedia PC's in my home so I can access and play any music, video or mp3+g (karaoke file) on any TV in my home. I can also browse picture files, watch TV channels. record anything on my TV like a personal video recorder and I can even surf the web using one of the remotes. No need for a mouse or keyboard- these are remote controls that look basically like your cable or TV remote does. The two I have the most experience with are the ATI Remote Wonder (not sure if you can play the karaoke files with the software that comes with it) and Snapstream's Firefly PC Remote (I know you can play karaoke through the software that comes with it). You can read more about both devices at their sites:
http://ati.amd.com/products/remotewonder/index.html
http://www.snapstream.com/products/firefly/
Both remotes have a USB reciever and both work best with ATI video cards (obviously the ATI remote wonder does). Both also use their own software designed with very easy user interfaces that you can customize or personalize according to your uses/needs.
Snapstream has a couple of different software applications that work with their remote. Their "Beyond Media Basic" program is enough to let you browse your files on your PC and play your karaoke tracks. You need to have winamp installed with the mp3G plugin too. Set the software to use winamp as your mp3 player and it will automatically bring up the graphics view when you play the music file. no need to open winamp or anything- Beyond Media Basic controls everything- you won't even see winamp open as it uses it's own interface to play the graphics/videos.
So these two remotes will do almost everything ya wanted except have the vocal off/on switch. I have used the ATI remote to access video/music files off my servers but haven't tried the karaoke mp3g's with it. The Firefly remote can do everything like the ATI remote will but I know for sure that it will play the mp3g files from your PC... I would recommend the Firefly remote definitely since i know 100% that it does most of what you want. if you decide to get one and have any questions on using it or setting it up, then just gimme a shout and I will walk you through and help as much as I can...
tig