I used to have a Netgear, and from what I remember it does port forwarding, not port redirection.
In other words: if you are connecting to the router from the outside world, and putting a :85 at the end (to denote port 85), the router will forward it on to the IP address of your Tivo - ON PORT 85.
So you need to have the following
1) Tivoweb configured to run on port 85, not port 80 (the default)
2) The entry on the Netgear say that for anything on Port 85, forward to the Tivo internal IP address (192.168.0.200 or whatever)
3) When you connect from outside your network (it will not work from inside it), connect to:
http:\\myname.homeip.net:85
If should work OK, assuming
a) you have registered "myname.homeip.net" with DynDns or whoever. Alternatively put in the IP address if you know it, but as it can change this is not what I would do.
b) wherever you are in the outside world, it lets you send traffic on port 85. My work will not, so I used 443 instead of 85 (normally reserved for secure http links, but who cares

)
Let us know how you get on