I've done my own waterslides for several of my marine forces.
I bought a starter kit from micro-mark (
www.micromark.com iirc). It includes a white transfer sheet, a clear transfer sheet, and a small can of decal fixative. They have a kit for laser and for inkjet.
I've done them on inkjet and laserjet printers, using the fixative each time.
I used photoshop, but you can use word, or powerpoint, or whatever software program you like. I imported a jpg of the symbol (I used a scan of a symbol) and then resized it several times, printed a sample, and cut it out to make sure it fit on the pad. Then I just copy/pasted the correct size symbol to fill the page. Easy to resize for vehicles as well, flip for termie pads, etc.
One caution, when I used an epson inkjet, it worked great. When I used a canon inket, it came out terribly, so the printer you use can have an impact on the final product. I would test print them as 'photos' on photo paper to get a sense of how it will look on the transfer sheets.
Let me know if you have any specific questions, I'll see if I can help.