I do that in a Pismo, a G3 500 with 256Ram, 10GB Hd and a 14" screen.
It is gonna be complicated to put so many things in a 12" but it is possible and fun.
The good thing is to have your 17" flat panel close. That is gonna be my next move, a 12" Powerbook with a 17" display.
Remember something about power & video: renders are allways slow, no mater what computer you have.
If you can make the same render in a 1/4 of the time now, for sure you are gonna do something to make it longer next time. The industry knows renders are slow.
The best move is to have 2 or 3 diferent computers. As we speak (write) I'm doing a render in my dual 500, it is gonna take about 1 hour and 20 minutes but I can go on doing stuff in my powerbook like spending time in macrumors

.
I have another Pismo but my girlfriend is using it to do her home work.
So, the best thing to do is to have one serious computer and 2 good ones.
When I'm in a rush I do my renders in the other powerbooks, once I was rendering with the 3 computers 3 different things and let me tell you that my set up is not expensive, 2 Pismos and a dual 500 that I'm gonna sell to get a 12" Powerbook in the near future.
Mobility and flexibility is where the power is.