Welcome to the forums!
There are lots of choices within your price range for a dSLR body and kit lens.
The Nikon D40 (6MP) with 18-55mm lens, Canon XT (8MP) or XTi (10MP) with 18-55mm lens,Olympus E-410 (10MP) with 14-42mm lens, and Pentax K100D (6MP) with 18-55mm lens all fall within your budget.
If you want to squeeze as much out of your $600 as possible, with as much room to grow as possible, I'd say the Canon XTi is the best choice. Since you don't know where your photography will take you, this gives you the most capabilities with the most room to grow. The kit lens is probably the least good of the kit lenses, but only slightly, and the Canons have more available lenses and accessories than any of the others.
Hope this helps.