New kid here

My intention is to purchase an M-Audio Quattro USB MIDI/audio interface and use it with Metro (in one or another of its incarnations) on my PowerBook G4 (1.25 GHz/512 MB/80 GB). I'll mix my existing instruments with some software synths and effects, I guess, but plan to phase in the new stuff gradually. Ease and quality of MIDI/notation integration are very important. Are there caveats that anyone can point out? How well would these products work together? Please forgive if this post is redundant. Any information will be extremely helpful (I'm looking to purchase within the week).
Peace,
Yaoski