The biggest limitations in Elements are the lack of a channels palette and its weird way of handling masks. It's really not much like using Photoshop at all, so if your goal is to get the PS experience, Elements isn't going to do it for you. In my opinion, the Gimp is more like Photoshop than Photoshop Elements is.

The Adobe trial versions are an unlimited 30-day license. No features of the program are turned off, as far as I know. I hadn't heard about a rental program from Adobe, but I know of a couple of other publishers that do that, so it's possible they've jumped on the bandwagon. A quick look-see around the Adobe site didn't turn up any information on it, though.