You need an image editing program.
The very best is Adobe Photoshop CS4, but it is very expensive.
A more sensible choice might be Photoshop Elements (current version is 8), which is Photoshop's smaller cousin - can't do all the same things, but it is much cheaper and perfectly adequate for most people.
Another editing program you can get is the Gimp (free and legal). It isn't pretty, has a big learning curve, but is a great program. http://www.gimp.org/
Or you can go to these free websites, but that option is nowhere near as good as having the program on your computer: http://www.picnik.com or http://www.picture2life.com/ or http://fotoflexer.com/ or http://www.sumopaint.com/ or http://aviary.com/
The last two are your best bet for more complicated tasks.
Lousy photos will always remain lousy photos, don't expect to do miracles, they do NOT happen.
The bit about not looking edited is entirely up to YOU. You will need to acquire some serious skills, then that part can certainly be done.
You will need to do a lot of reading and learning - those skills don't happen without effort. Luckily, there are lots of resources available to help you. Start by reading the program's helpfiles, looking for online tutorials, and checking your library for books.
Having said all that, I would start by learning about photography first, THEN worry about post processing.
Learn about your camera !!!!
Read your manual !!!! Read it several times, and practice in between.
Attend a class, read some books, read/watch online tutorials.
The major camera manufacturers (like Canon, Nikon, Olympus etc) all have very useful sections on their website for learning about photography.
http://www.usa.canon.com/dlc/controller?act=HomePageAct
http://www1.nikonusa.com/slrlearningcenter/index.php
http://www.olympusamerica.com/cpg_section/oima_learn_center.asp
Understanding at least the basic principles of photography (as well as being familiar with your camera) will enable you to make the most of your gear, and will make a HUGE difference to your images.