Printing isn't as much of an issue as many folks make it. For black only decals, I have a cheap laser printer- works fine on regular decal paper. I do know some folks using the inkjet paper, they get reasonable results. What I do for colored decals is print on regular paper, and take printout and decal paper to local print shop for copying with regular color copier. Works fine- he charges me 80 cents for copy of full 8.5 x 11 sheet.
Even with laser or copy shop copies, final decal MUST be overcoated. Even laser print/copies are fragile. I use Testors glosscoat or dullcoat, but there are other solutions you can overcoat with.
I learned how to design decals two years ago, and it is a blast! There are two main routes: bitmap graphics (GIF, JPG, BMP, etc) and vector graphics. I knew bitmap, but learned vector for designing decals. Now that I know both I advise you strongly to learn vector graphics. It is so much more powerful and easy once you learned the trick. Go for CorelDraw, Adobe Illustrator, Canvas or the like. You can download 30 days trail versions of all of them.
A bitmapped image creates a two-dimensional array, a grid, and fills in the value of every part of the image with the color value for that square of the array. As many words are needed as pixels in the array (three words per pixel for color images).
A vector image is like a graph. The program records two numbers (x and y values) for the start of each line, two more for the end of the line, and one to three lines for color of line.
If lines are drawn defining a box or any other closed figure, there can then be a color associated with the interior of the figure, to "fill" that area with color.
Generally the vector file has a much smaller data size for storage concerns. Since computer memories are getting so big, this is not as much of a problem as it used to be. The other big advantage is that vector images can be easily edited to redo text or whatnot. While bitmapped images can be edited, it is generally much more work.
Outside of storage space the main advantage of vector graphics is that they can be infinitely re-sized up or down without affecting image resolution, the only change being the scaling factor. With bitmap images the resolution limits how much the image can be re-sized upwards without losing detail.
The next discussion will cover Illustrator versus Photoshop ;-)