Just a quick comment ...
You didn't mention what kind of Mac you have, but the Tech Requirements looks like it requires a dedicated video card.
So Macbooks and Mac minis are OUT.
ft
This is not true. It makes use of the graphics card for faster processing, but does not require a card. You can download the trial version yourself, and I am running that on a MB 2.2 w/4GB RAM and a 7200RPM Hitachi 200GB drive. Aperture is performing very well w/2000+ jpeg images in the database. So, it does NOT require a graphics card for basic use.
For mrogers --
Aperture has some really cool tools (how it manages key words, the loupe tool, better red eye and other photo adjustments. Also the way it presents full screen edit mode, with the floating inspector is REALLY cool) but most everything you want to do with basic photo development can be done w/iPhoto. I also noticed that the recent iPhoto updates have helped w/performance (especially with iPhoto issues around sharpening, noise reduction, and others).
The real strength with Aperture is in how it handles and manages changes to work shot in RAW. If you are planning on using RAW format, you won't be happy in iPhoto. Download the trials of Aperture and Lightroom to see which you like better (they are designed to do the same thing, but work in very different ways, so you have to try them both).
My take on Aperture 2.0 vs. iPhoto to date (I'm a hobbyist not a pro, and just getting into RAW): if you shoot in jpegs, then iPhoto will work for you BUT if you like toys and have money, Aperture looks like it's ready for anyone to use now and the full screen edit mode is tres cool. If you use RAW, you'll need to move to either Ap or LR. My only caveat with Ap 2.0 is that it hasn't been out long enough to be "stress-tested" in terms of performance with a big database. So, you can always trial, but you might want to monitor forums to see any feedback on performance.
For OP -- By now, you must know Ap 2.0 will do what you are looking for re:.mac, but it requires Leopard 10.5.2 and prefers better, newer hardware.