If you download the 30 day trial use version 1.4.1, not the 2.0 beta.
Unless you have a Licensed copy of LR you can't play with the Beta...
Also before you start with Lightroom check out some of the tutorials on the web. If you've only got 30 days to decide if it's for you then you need to make full use of the time available.
Lightroom although designed to work with RAW files will also handle jpeg images
Current price for Lightroom is about £190. However as the version 2 incarnation is due in a few months ( No date from Adobe yet) may be worth hanging on, as there is no indication about free upgrades for recent purchases.
A 30 day version of Photoshop and Elements is also available from Adobe as well
If you've never done any image manipulation work before you may find Photoshop a bit overpowering as is the £500 price tag. Elements has a lot of the features of Photoshop, but at a tenth of the price, and may be a lot easier to use in the first place.