Cojo,
Xeep is correct in what he said. Screen Spanning Doctor will allow your iBook to run even with the lid closed.
However, a few users have mentioned that heat is released through the keyboard. If your screen is against the keyboard while it releases heat, the screen could be damaged.
Also, your hard drive isn't invicible. Yes, it is protected inside your machine, but a couple of hard knock on a spinning disks can mean death.
So it's up to you. If you're willing to risk damaging your machine because you don't want to use your CD player (or can't/won't buy an iPod), give it a try.