I have the Tascam GT1-mkII portable Guitar Trainer, which sounds similar to what you guys speak of, except it's portable so you can take it with you wherever you go. They also sell a case with it that has built in speakers, so you not only don't need to lug around headphones with you, but the Tascam is protected, AND it has slips for around 20 CD's. It's pretty cool. You plug your guitar right into the thing, and start playing along to the CD. You can slow them down, speed them up, loop certain sections, all without changing the pitch. You can even change the Key the song is in if you want to, which is pretty weird. It also has a bunch of guitar effects, so if you want your guitar to have a phase, crunch, or delay or whatever, you can add that.
Play music, expand the mind, inspire...
"We must embrace pain and burn it as fuel for our journey" - Japanese poet Kenji Miyazawa