upgrade from 8.0.3 to 8.1.0

Hi,
I have enough resources on my 3 postgresql servers to run more than one
instance of postgres.  Is there a way to keep my production db up and
running in 8.0.3 while I also run 8.1.0 on the same server?   Then, I could
copy the data and support two databases until things looked good.  Then, I'd
shutdown 8.0.3.

Thanks,
~DjK