Been Away

Hi, All- I've been away from the biz for awhile and need to know whether or not it would be more affordable to upgrade my hardware and software in small or large increments. Both components are dinosaurs: Power Mac G4, Dual 500, only 1.5G RAM, Pro Tools LE 7.3.1 cs8. Interface is first model. Would like to upgrade to PT 10 HD or 11 HD. Probably looking at buying a whole new machine as I'm migrating from simple song-writing/composition to audio/film composition. Any advice would be helpful. Thanks. :-)