i think you're hurting yourself using a Macbook as your photo editing computer. only because the entry level Macbook is a very small LCD, and is not designed for professional photography work.
i'm guessing you prefer the Mac OS and thats why you're only looking at Macs. if you're serious about photographing professionally, look into getting a LaCie monitor. Apple displays are great for general purpose use. but for photography you really need to look into a monitor, with true color representation and uniform contrast/brightness.
maybe get the laptop first then save up for a nice display. even though Apple makes a great general purpose display. you will see a difference between the colors on screen, and the final printed product.
good luck
