I solved the problems myself... and here's the solution in case anyone else would like to keep $89 in their pockets!
In both instances (remote access to work and connecting to the TiVO network), it is indeed the Port Forwarding feature you need to use in the Versalink 7500 router setup website (people will try to disuade you of this!). In both cases, I did the following just using different port numbers (depending on what I was trying to get my computer to talk to) and with my computer's firewall on and the router's firewall set to medium. Sorry I couldn't figure out how to post screen shots in this post... prepare to visualize!
1. On the "New Port Forwarding Rule" page, click on "create" for #1, pick "host" for #2, and then select the computer your router is connected to in #3 (it might work with one of the other computers selected, but mine worked with the device he router was connected to).
2. You need to do this step twice - first time select "direction" IN (in #3), second time select "direction" OUT. On the "Create Port Forwarding Service" page, you can name it whatever you want for #1, keep "port forwading" selected" in #2, in #3 you'll need to figure out (a) if you need to select TCP, UDP, or BOTH for "protocol" (based on the online or manual documentation for the system you're trying to connect with), (b) "global portstart" (c) "global startend" and (d) "base hostport" should also be found in the documentation (see note below for Windows remote access and TiVo port info that worked for me) and they are all the same number (ex., global portstart = 80, global startend = 80, and base hostport = 80), and then (e) select the direction (first time, in; second time, out... remember, computer communication is a two-way street, just like humans!), and (f) leave "port direction" as DST. Then you need to (g) click apply after you've added all the ports in both directions (my screen started this sequence of freaky flashy glitchy behavior, but apparently that was the fairy dust making the computer magic happen b/c when it was done, my connectivity was restored!).
3. The port that worked for me to remote access from Windowss PC to Windows PC was 3389.
4. This is the site that had the big list of ports for TiVo, but I think it was ports 80 and 8080 (see the first entry under the troubleshooting port issues) that made the magic happen for me: http://support.tivo.com/app/answers/detail/a_id/402/c/105%2C109/r_id/100041
I hope this is useful to some others and that you just saved yourself $89 in tech support charges for this irritating little issue... go buy yourself a drink and enjoy the summer! 
Now I'm off to figure out how to back up these router settings based on the less-than-friendly-to-laymen-computer-users Versalink manual. Wish me luck!