johnr1969 - You can change the DPI in paint programs which will help to some degree, but I wouldn't enlarge the render in one of these as you will definitely lose quality, so rendering on a VERY large scale within Vue would be the only answer. If you have spectral atmospheres, poser figures & hair etc then this render would take an age, especially if you use user settings with high AA as you would probably need for close up detail. Rendering from more than one computer will certainly help. 
I'd also be interested to know about commercial rendering facilities over here, I did see one once but I can't remember the link.