Loves my Macs (mostly), me - I used a Powerbook G4 for live location recording for years and it never once let me down. If you can keep it as 'just' a recording machine (i.e. keep it off the web as much as possible, leave the Airport modem turned off, only install what you actually need for making music) you should find that it doesn't fall down, will run quickly and easily with any peripherals you see fit to connect to it, and has the added bonus of a sh!t-hot built-in audio engine.
You'd get one of the last generation of Firewire-equipped Macs (personally a must to leave your outboard options open) relatively cheaply, max out the RAM and it should do you sterling service for years to come.