You should be able to keep your music collection on your iPod alone (and not on your TiBook) and still be able to listen to your music on your TiBook through your iPod (when connected of course). My girlfriend has a 20G iPod, and a Graphite iBook. She has about 15G of music on her iPod, and keeps none on her iBook. When she wants to liseten to something on her iBook, she just connects the iPod.
I would strongly suggest that you have some sort of backup of your music if you're going to do this. iPods are rugged, but something that gets that much use and abuse is going to run into more problems than usual. If for some reason your iPod gets funked, your music is gone.