image size

Dear useRs,

I'm working in R 2.0.1 for Windows and producing PDF
files with Sweave. I seem to be hitting an image size
ceiling of around 6.8 x 6.8 inches.  I would like to
produce taller images to make better use of my A4 page
and have tried:

<<TestMap, fig = TRUE, width = 6.5, height = 8 >>=
par.old(fin = c(6.5, 8))
image(x, etc.)

I get the message:
Error in plot.new(): Figure region too large

Is there anything I can do?

Mikkel