depends on what youre doing with it specifically.
in any case. be sure to get a gig of ram (or more), an external firewire HD and a firewire audio interface (i have a firewire 410) and you should be golden.
even with the 1.33ghz model you should be fine considering logics freeze function - will render an individual track and free up any software synths or effects that is holding your CPU down.
for simple multitrack recording any of the powerbooks will be more than enough. adding softsynths or lots of higher quality effects (especially reverbs) without freezing tracks - thats where you could get into trouble.