Oh gosh I'm sorry, somehow I missed your last message, or I would have written the instructions already. But at least by now I've had a chance to review your project, and investigate (somewhat), the extension which Moini mentioned.
Yeah, I'm not installing that extension. At least not right now. There are some extra things that have to be installed, and I'm just not up for that at the moment.
But for your project -- if the label itself is in a raster format (PNG, I think) it might be better to use a raster graphics program. Does your printer require vector contents? If not, then Inkscape might not be the best program.
Ok, find out what kind of file you need to send the printer. If you need vector contents, I'll be glad to write you some instructions. If not, I would suggest using GIMP (I don't know much about using gimp, but I'm pretty sure it has a tool or feature that will do this. I don't have a link, but I think there's at least one forum for gimp users.)