Questions on computer software/hardware sequencer!

I just got an "eMac" 1.25 ghz with 512 mb ram. I already have an MPC 2000xl and a Roland xp-60. I am a beginner who is interested in doing some sequencing and recording via computer, I just need some ideas of what else I shoud get?

I am looking at the MBox 2 pro (I heard pro tools is the way to go), I have never used a computer sequencer or software/hardware before. I would appreciate any advice I can get.

Thanks!