if you want to dig into photography while keeping the interface simple, get ahold of Photoshop Lightroom 2. Its only about 100$ and is an amazing tool for photography. I used only Lightroom to edit all the below images; which were taken with a Rebel XTi (the model previous to the XSi), but used a nice zoom lens (70-300mm IS USM).
more:
http://img7.imageshack.us/img7/6696/mg8936.jpg
http://img7.imageshack.us/img7/9468/mg8972.jpg
http://img7.imageshack.us/img7/9950/mg8946.jpg
http://img7.imageshack.us/img7/446/mg9122.jpg
http://img7.imageshack.us/img7/4325/mg9150.jpg
http://img21.imageshack.us/img21/3853/mg9275.jpg
http://img7.imageshack.us/img7/3787/mg9301.jpg
(shot at D1GP in Anahiem)
Pretty much all of the editing done here was with the contrast, saturation, recovery, blacks, and fill light tools.
Good post processing is made much easier with good pictures though. Learn your basics for f/stops and exposure settings. I generally shoot in apreture-priority, shutter-priority, or full manual, but you can always use the auto settings as kind of a guide for roundabout numbers on what the camera thinks is best for a given situation. A really low number f/stop will give you a smaller depth of field and make backgrounds much more blurry and the subject pop out more. A slower shutter speed can introduce implied motion if the subject is stationary and the background has motion blur. There are tons of tricks and tips available. If you don't want to look online, Scott Kelby has a fantastic book series which is well worth looking into.