How do I set up multiple RDPs thru my sonicwall TZ170 firewall

You must open port 3389 to the internal IP address of the machine you want to connect to. This means creating something called a PORT FORWARDING or PORT MAPPING. The protocol to choose is TCP and the port, as mentioned, 3389. Then simply point that to the INTERNAL IP address of the machine you will be controlling (it is on the internal LAN, behind the firewall).
Then from a machine outside simply connect to the external IP of your SonicWall using the RDP Client (MSTSC.EXE).

Claudio Rodrigues

Microsoft MVP
Windows Server - Terminal Services

There are 2 common methods:
1- You can change the default listening port for remote desktop. Remote desktop by default uses port 3389. By changing a registry entry you can change that default port. It is recommended you separate the ports by 1 or 2 so you would have a configuration as follows:
Computer #1 on the router forward port 3389 to port 3389 on IP 192.168.0.101
Computer #2 on the router forward port 3391 to port 3389 on IP 192.168.0.102
Computer #3 on the router forward port 3393 to port 3389 on IP 192.168.0.103
Computer #4 on the router forward port 3395 to port 3389 on IP 192.168.0.104
When connecting from the remote site in the connection window of the remote desktop connection manager you would enter the WAN IP and the port #, separated by a colon such as:
  66.66.123.123:3391
Instructions on changing the listening port can be found at:
http://www.petri.co.il/change_terminal_server_listening_port.htm

2-If the Sonicwall supports forwarding an external port to a different internal port, as some routers do, you can eliminate the changing of the listening port. Simply forward a desired external port such as 3391 to internal port 3389 on the desired machine. The user will then still use 66.66.123.123:3391 to connect, but it's easier to configure.

If by any chance you are using Small Business Server, the proper way to do this is with it's unique feature; Remote Web Workplace. See:
http://www.lan-2-wan.com/SBS.htm#q1

Thanks capital_printing.
However the actual answer you accepted is really not a solution at all. You can ask the moderators to reopen so that you can re-grade. If doing so, in my opinion it should at least be a point split with tsmvp.
Cheers !
--Rob