If portability is the most important attribute for you, then the 17" is not really a good choice. The best balance between power and portability is the MacBook Pro 15.4" - I have one as my main machine and it is very workmanlike. (Of course, if Apple still made the 12" G4...)

This, with Leopard and Boot Camp, can also dual boot Windows, and most decent strategy games can therefore be played on it - ie all the Totalwar series to date.

Then there's the new MacBook Air - what looks like a stunning design, but I haven't had a chance to play with one yet, so no recommendations. With Apple, much like most computer manufacturers (but more so) it is usually best to wait a few months for version 2 of their brilliant but flaky products.