I'll guess that you're coming into the first computer from
outside your home network and assume both are running XP
Pro.
If you are not using a router, I don't know how to do it.
If you are using a router, you must have opened up port
3389 and directed it to the first computer as a "virtual
server". The solution is to open up a second port and map
it to the second computer. Then configure Windows Remote
Desktop to listen on this port.
To have Remote Desktop listen on a different port on
computer two, open Regedit. Be very careful as always
with regedit. Now dig down to
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Termina
lServer\WinStations\RDP-Tcp\PortNumber and change the
number to whatever you set up on the router. Reboot and
you should be all set. When you come to access computer
two from outside, use the other port number (eg. if you
normally type 123.123.123.111 to get to your first
computer, and the new port number is 555, type
123.123.123.111:555 to get to computer two).
Full instructions are at
http://support.microsoft.com/default.aspx?scid=kb;en-
us;306759&sd=tech
Best regards,
Steve