1. If you want to do particularly good renders, it'd probably be best if you got a 3D graphics program.
2. Photoshop 4? Not much beyond the basics there, I could show you how to do all sorts of fancy tricks with the standard aspects of Photoshop, but it'd take me several inconvieniently long months to teach you a good base of useful knowledge, and even that's useless if you haven't learned a good deal of the ins and outs yourself- direct experienceis the only way to properly learn almost any graphics app.
3. If you want to start simple, get a handful of plugins, learn to use the filters, Dodge, Burn, and some of the faders, and cut-and-paste.
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Purveyor of spurious wisdom.