Pro Tools LE + M-Audio FT C600, REAL system requirements

[Feke]

Hello all, I'm new to both this board and using computers for music production so I'm sorry if I'm asking silly questions.

Anyway, I bought the M-Audio Fast Track C600 sound interface bundled with Pro Tools SE yesterday, and I'm having surprisingly big problems to get it all working on my computer. I've been following several guides how to optimize the computer for Pro Tools but I'm still having trouble getting it to run well with Pro Tools. After 3 tracks of audio with guitar amps as the only plug in effect the computer pretty much dies on me. I've been using porta studios up until now so I've never really understood how taxing this is for the computer.

My computer is above the system requirements on the box though, so my question is:
What is the REAL system requirements for Pro Tools SE to be able to use the program as intended?

I was planning on upgrading my computer anyway so I just need to know what I should be aiming for.

What about an iMac with 2.7 GHz quad-core i5 CPU and 4GB of RAM, would that be enough?

Edit: Sorry for the misspelling in the thread title. It should say Pro Tools SE.