From all I have been told by DW personnel (which is not in any way the final word on the matter) one would have to have the "Professional grade" service they offer to use any type of vpn or remote desktop reliably. They claim they don't block any ports TCP or UDP, which I have found to be true as far as I can tell. The biggest problem is a result of their invisible proxy. There is no way around this that I am aware of. I have been told by a DW technician (although I claim the previous disclaimer concerning DW personnel as well as a pretty difficult language barrier between myself and the outsourced technicians they employ) that they actually have less IP addresses than customers, so a person's IP address changes on a regular basis. There also seems to be some huge latency issues within their NAT servers. I've been able to telnet into my DW6000 router, but the options there offer no hope of bypassing either choke-points. To telnet into a DW6000 use port 1953. This does come in handy when the modem locks up and needs to be reset. Just give it the command "rr" (minus quotes) and press enter. The router will reset itself without you having to physically go to the router itself and unplug it.
All in all, DW's offerings are pitiful and they make no effort to remedy the problem either. However, for your company and mine, they are the only option and they have to know that. At least download speed isn't too bad. I am able to get about 80kB/s download in real-world applications with (a) fast server(s). If you figure a way to rid yourself of some of the NAT/Proxy complications, I'd greatly appreciate the info. Meanwhile, I will be giving gotomypc a try.
Hope this helps,
-John