'Morning Drkwarrior . . . 
When you first start a new project select, “Document / Modifiers” & change the "Width = & Height = " to what ever size you wish to work in. That’s the first step. When your image is complete, export it to where ever you want to save it. Open Paint Shop Pro & import the saved image. Select “Image / Resize”, select “Actual / Print Size” & set your resolution to “300 dpi”, then set your “Width & Height” in inches, to what ever size you want, set the “Resize Type” to “Bicubic Resample” & choose OK. After a few minutes you’ll see the re-sizing completed & you’ll have a picture that you can print or what ever you want to do with it. 
PS: ( The larger the canvas size in ZBrush, the more image information you have to work with in you image editing software. )
Hope this helps some & have a good one . . .
Mark.