Greg,

I recently made some of my own decals. I bought some Testor's decal paper from my LHS, scanned color pictures of the markings I wanted from a reference book, uploaded them on my computer, put them into MS Paint, and then played with the size by enlarging/reducing until I got the size right (I printed them on paper and then held them up against the completed tank).

Once I had the right size, I printed them on the decal paper off my inkjet printer set to the highest resoltion and let them dry. Afterwords I applied two coats of Krylon clear coat. After drying, I cut and applied. I got a super custom look on a custom scratchbuild project. I'm very happy with the results.