I own a 12" PowerBook with a GeForce FX Go5200 graphics card. For whatever reason that I've yet to discover, Apple has declared the GeForce FX Go5200 'bad' as far as Aperture 2.0 is concerned, and attempting to install it results in the message: "Your video card does not meet the minimum requirements to run this software." By the time I figured this out, a copy of Aperture 2 was already enroute to my house...
Of course, there's always a workaround. The following instructions apply to the retail version, and should let you install Aperture on any type of Mac, not just the 12" PowerBook. I doubt Apple will provide support in this case, though. I'll leave it to you to figure out how to do the same for the downloadable trial.
Here's how I installed the retail version on my 12" PowerBook:
$ mkdir -p /tmp/aperture
$ cp -r /Volumes/Aperture/{Aperture.mpkg,Packages} /tmp/aperture/
$ open /tmp/aperture
You should see Finder pop-up with the contents of /tmp/aperture<installation-check script='installationCheck()'/>
Insert a pair of <!-- and --> (HTML comment markers) in the appropriate places:
<!--<installation-check script='installationCheck()'/>-->Mac OS X Hints
http://hints.macworld.com/article.php?story=20080308153412349