For vector stuff, I don't really know anymore. I used to get along with Freehand quite a lot, but that must now be almost 10 years since I last used it "properly". I'm also completely out of what's happening on the PC software scene. I've also used Fireworks, but that's more for web-graphics.
Photoshop should still be able to do it, it's just that it's not really built for it.
Corel Draw used to be quite sweet, about 20 years ago.
I guess just do a search for vector graphics software?! What you want to be able to do is, to create a box, and it remains a box, not pixels.
http://en.wikipedia.org/wiki/Vector_graphics_editor http://en.wikipedia.org/wiki/Vector_graphics If you have it all in vectors, then you can export it to an EPS or something which would allow the company that does the decals to cut them out with perfect precision (as there's no degradation in scaling).