It doesn't sound like you need Aperture at all. iPhoto should suffice, even if you're using some RAW.
That said, I shoot all RAW, and use PS CS3, and Aperture 1.5.3, and I'm running a BlackBook @2.00 ghz with a Core 2 Duo, and 2 gigs of ram, AND a seperate display, and it runs it beautifully.