> What I am trying to do is redirect traffic sent to
> ghostpriest:8000 over to cube:80. (Cube being a machine on my internal
10.*
> network)
> ---stuff---
> As far as I can make out I need
> something like
> rdr le0 0.0.0.0/32 -> cube.my.lan ports 8000 80 tcp

The following should work:

rdr le0 0.0.0.0/32 port 8000 ->cube.my.lan port 80 tcp

where le0 is your external interface.

Hope this helps!  Mike.