It all depends on what you really want to do.
If it is just scanning, enlarging and printing than the software which will come with your scanner will be more than sufficient.
If you want to go into real photo editing etc.....than join the discussion groups. A phantastic tool is Paintshop Pro. I myself prefer Corel and the annual package of Draw and Photopaint.
If you just want some neat effects, there are plenty of free or shareware programs around which will do what you are looking for.
The Office2000 package has PictureIt included, my slide scanner had PictureIt bundled with it.
My flatbed had PhotoSuite with it.
Obviously you are new to this area of digital reproducing, just find a scanner which suits you and use the package which comes with it. Soon you will find out what you like and what you are missing. Than take the next step.