I know in the past that people have been able to download a trial copy of the current Photoshop from an Adobe website. The trial expires after a month, at which point you'll need to put in a key code. You can obtain one by purchasing the program legally, or, yes, you can obtain one illegally online. Keygens that are downloaded from P2P sharing programs will often also come with a virus, which might tank your computer or might just sit there dormant. I don't know if trial versions of PSP are offered; I've never used the program as about 95% of the graphic artists I know - professional and hobbyist - all conclude that Photoshop far outstrips PSP. You may want to try both on trial if you're curious about their capabilities, to compare and see what meets your needs. What you likely will not want to do is invest your money in Photoshop Elements. It's a fantastic photo editing program, but is limited to pretty much that, photo editing. If you want change the general color of a photo, get rid of red eye, etc., it'll work just fine; if you're looking to do more sophisticated things, you need a more sophisticated program.
Also consider if you're going to one day want to do more with your graphics; Adobe offers a wide range of excellent other programs, In Design, Illustrator, Flash, Dreamweaver, and Fireworks, or, all of the above plus Photoshop in the Adobe Creative Suite. To shell out for the entire creative suite is a painful experience, but if you are planning on making money using the software, consider it an investment in your business. :)
Lastly, I would recommend checking out the new features that will be offered in cs5. Some of the verbage might be confusing if you don't already use some form of Photoshop, but you can surely see what they're achieving on the screen, and it's pretty darn neat. Right now, the best estimated release date I've heard is sometime around April/May 2010; if those features really interest you, you may want to hold out until the release, rather than purchase/download CS4 only to upgrade/re-download in five or six months. :D