Working for the liberation of all beings everywhere. Bringing higher consciousness to the planet, one eternal moment at a time.
Remember, you are not legally entitled to sell any recordings made with such tracks, and many of them are covers of well-known songs, so unless you're willing to pay for the duplication rights, don't publish a CD with these on it. However...there are downloadable legal backing tracks online. Just because it's a cover, not the original artist, it don't mean ya get to use it free. Incidentally, you might give the dude who did most of these tracks a few euros to help him continue his work. He has a paypal account ... a couple bucks won't hurt ya, and this guy works hard for what you're using.
Most importantly, play short simple phrases, and don't be afraid to take the harmony parts.