Welcome to Photochopz
Photoshop CS3 would be your best choice for photo manipulation. If you don't feel like downloading anything quite that large (450+ Mb) then you may be interested in something smaller, such as Fireworks MX 2004 (~27Mb). Fireworks has far less of the features photoshop has, but retains most of the essentual tools you'll need. It's also set out in much the same way, enough so that a photoshop user could use it effectively, and with ease, right from the get go. From there, either play around with everything until you understand what it does, or learn about it on the internet.
http://www.soft32.com/download_351.html (Fireworks trial)
https://www.adobe.com/cfusion/tdrc/i...&promoid=BONQJ (Photoshop trial- requires creating a free adobe account)