I use this Setup quite often for my "travel" Catalyst. It works flawelessly with a THTG, but depends on what you're doing.
Absolutely necessary is an external HD via Firewire 800 which serves your Content.
My MBP ist the 17" with a 7200 rpm HD, external HD also 7200, 3Gigs of ram, and the fastest Processor.
Resolutions of 1024 x 768 work, 3 movies in dv codec and 640 x 480 work also parallel.
Layhers Window must be closed for Playback as it eats up additional Power.
Grafik FX also eats up processing power.
At least you need to play around with it to see, what can be done and whats not. For me many applications fit with this Version of Catalyst
Best
Rolf
www.chaoscenter.net