Sonicwall(in transparent mode) VPN with DSL router.

I don't know where to start. I inherited a client that has a unique setup. The VPN is activated on the firewall, but I can't access it. I am new to this WAN/Firewall/VPN stuff so I am no IP expert, barely a beginner.

Setup is

Workstations and Servers >> SonicWall TZ 170 >> DSL Router >>Internet >>Cable modem >> Lynksys router >> My home PC

The sonic wall is in transparent mode so I think NAT is disabled and the DSL router does the NAT and DHCP.

The sonic wall has the VPN license and it is enabled. I have the client on my home PC. It just doesn't connect via the public address.

Here is were my knowledge is lacking. Do I need to open ports on the DSL router? Which ones? Will the sonic wall vpn work if NAT is being done in the router?

I wouldn't mind forgetting about the VPN if I could Remote desktop in, but I forwarded ports 3389(on the dsl router) to a static pc and that didn't work either. Then I tried to forward the dsl ports to the Sonicwall then making a rule forwarding 3389 to the static pc, but that didn't work.

I think I lack a few pieces of knowledge of whats going on with transparent mode and how the router and firewall react with each other.

If anyone could give me any insight i would appreciate it.

VPN was never working. I don't think protocol 50 is being passed, I am not even familiar with what it is. How do I setup protocol 50?

If the sonic firewall is acting as a bridge will it stop the port forwarding from the dsl router. If I could get RDP going I could support their emergencies while I research and figure out the darn VPN.