you need to get it working on your local lan before you try to get it working via the port forwarding.

1. Connect your n900 to the lan via wifi, test it can browse the internet.
2. Create user on the windows desktop with password and add them to the group to allow remote access.
3. find the ip address on the windows workstation. start, run, cmd<enter>, ipconfig<enter>
4. run up remote desktop on n900 and create session for the workstation IP address.

make sure you turn off windows or other firewalls on your workstation first while testing.

hint: use the windows event log to locate any workstation related issues.

rgds