It depends what you mean by composite. If you're just talking about 3 or 4 simple layers "roughly" stuck together, then HSBN is right, use GIMP, it's free and fully capable. I say roughly to imply just cutting something out and sticking it on another layer. I don't mean to belittle it, this is fine for most peoples uses. And if you're asking this is probably sufficient for your needs. Just get GIMP, don't waste your money with Photoshop.
But people who really composite take it to much, much more complicated levels. When I composite I will have many, dozens, of intermediary layers of adjustments for each composite layer to realistically pull my layers together. By then end I can frequently have 50+ layers in a composite, the final working file being over the 2GB limit. It takes a powerful program and a powerful machine to run this level of computing. I've never used GIMP, it may be possible to composite at this level, but Photoshop Elements is not, you need the full Photoshop if you really want to get into the art.
