iPhoto is a capable photo manager and editor. i suggest using this one to start off because i think it's best to keep things as simple as possible. otherwise, if you let things get complicated, you can become distracted and loose sight of your initial goal. that is to become more serious about photography and a better photographer.
you don't want to allow yourself to become so overwhelmed by all the new toys and their latest and greatest features. for example, i have photoshop cs3, and the only features i've used frequently to edit my photos are the burning and dodging, sharpening, layers, masking, and sometimes enlarging and cropping tools. for me, sometimes i don't even used any of them. most photographers have limited themselves to these few tools because they took extra care to compose and meter before making the shot. let this always be your primary goal so that what ever photo manager-editor software you pick, you know that you're the master of your photos, and not the latest and greatest software.