Obtain karaoke software or a CDG disc duplicator to rip songs from a music disc and burn them onto your custom CDG disc (see Resources). Pilot Karaoke sells reasonably priced CDG drives and karaoke products for your computer. Power Karaoke software is also a good choice for burning your CDG discs.
Purchase CDG discs only. This will allow you to embed lyrics with your song tracks that will appear on a screen during playback. If you purchase any other kind of disc, you'll still have your sing-along track, but lyrics won't be available.
Use AV Video Karaoke Maker to add lyrics and graphics to karaoke music tracks you purchase and download without sing-along lyrics (see Resources). This software allows you to add lyrics by simply dragging and dropping a text file onto your karaoke track.
Consider using an online service that will make a custom karaoke disc for you. ExpressKaraoke is one such service (see Resources). These services have many premade karaoke discs, and they can compile a disc based on your requested songs for a reasonable fee that will include lyrics.