Chris is correct; the concept is simple but the execution can be a bugger. I've been a graphic artist for 25 years and I have plenty of experience cobbling things together with what's on hand, but there are some things you may as well forget about, and making anything but the most rudimentary decals on your inkjet is one of them.
I checked eBay this evening, and I could get an ALPS 5000 for $500 or less. Since it appears I'm going to be making a bunch of decals I think I may as well invest in one; it'll do 90% of what I send out to be printed, and I'll have a lot more control over costs and delivery times.
So c'mon fellas -- order a bunch of pricey decals from me so I can buy that printer!