I used to run AE 7 on my MBP, and it worked pretty good. It is a bit on the slow side, but as long as you have a decent amount of RAM, you should be good.
How much ram do you have in your MBP? Both After Effects and Rosetta are RAM hogs, I could see trouble if you're using them together... especially with under a gig of RAM.
How does C2D and CD compare when using After Effects? As long as rendering 1 minute doesn't take like 15 minutes... back in the days of G4 and FCP *sigh*
I used to run AE 7 on my MBP, and it worked pretty good. It is a bit on the slow side, but as long as you have a decent amount of RAM, you should be good.
How much ram do you have in your MBP? Both After Effects and Rosetta are RAM hogs, I could see trouble if you're using them together... especially with under a gig of RAM.