Ah, AoE3. Second only to AoE2.
I run the Mac version of AoE3 on a Macbook 2.0 Ghz with GMA 950, on close to minimum specs (you can crank them up if you aren't playing online), and a 20-inch 2.4 Ghz Intel 2008 iMac, with max specs (I play LAN games with the two, against AI usually). Get the PC version if you already have Windows installed on your Mac, because you can do all the mods, custom random maps, custom AI's, and scenarios, a lot of which are easy to make work on a Mac. You can also play with other Windows players.
If you don't have Windows, you'll find a few minor bugs and annoyances (villagers and units getting "stuck" inside trade posts, for example) with the Mac version, as well as updates that do come a little slower. It also takes a bit more power to get the same performance. But you should be happy.
I also play AoE3 at LAN parties at a friend's house, who has 5 PC's (some quite old, and running minimum specs. There's quite a bit of lag, but there's nothing quite like a 5-player game with friends (and family) you know, all playing in the same room.
Anyway, with your MBP (not sure what graphics card you have, but assume it's the newest one), you should be able to run it max specs with no lag or any problems. Again, you'll get a little bit better performance in the Windows version, but not too much to matter.
Enjoy a great game, and one of my all-time favorites.
