DTV decided to send me a newer DVR that is internet capable. (Much appreciated BTW!. Good Customer service)
I did the same thing you want to do so I know it works. There are a few "what if's" involved. For instance, Is your Wireless an Infrastructor or Ad-Hoc. Also, Do you use static IP's or Dynamic (Not to your ISP but Internally).
MY example. The directv tech couldn't help so I decided to experiment myself. I have static IP's on my LAN. I also have a "server" so I have an "infrastructure" configuration. Using a Netgear router to the Internet and a wireless Linksys router connected to the DVR. After much experimenting, I found that changing the Linksys to "Ad-hoc" (yup, even in an infrastructure setup) the Linksys connected to my Netgear perfectly. Effectively turning the Linksys into an Access point.
Once you've configured your routers (and CAN ping the router connected to the DVR from any other computer), Don't forget you need to configure your DVR through the menu on the TV. It's really easy BUT, If you're using Static IP's, You need to give the DVR an entirely separate IP. ie: 192.168.0.???.
If I can help, Please feel free to ask.