Single frame subregion parameter for batch render.

[Robert Cole]

I need to render individual tiles of a very high resolution image (and 
stitch them together after, most likely w/ Photoshop). I can no longer 
find the documentation on Image Resolution>subregion parameter for batch 
rendering..anybody have a hint?  And, if anybody would like to chime in 
on another, possibly less tedious way of rendering out and saving 
individual tiles , I would be very grateful.  (The requested image is to 
go on a 20' wall...)

Thank you,
-Robert