Do you have a router connected between your DTivo and your PC? If so then you need to make sure your default gateway IP matches that of the router. It's the same address specified in the manual for connecting to the setup screen of the router via ethernet connection. The broadcast IP is the same address with a 255 at the end.
If you don't have a router and are connecting to a hub or switch, I'm not sure if you need to specify a broadcast IP or default gateway. Networking isn't my strong suit but it seems to me that if you don't have a router then these IP addresses are meaningless and may end up causing more harm than good (or possibly have no affect at all). Keep in mind that this is purely conjecture on my part and I'm just thinking out loud so don't take any of this as gospel. I'm sure someone with the right know-how will point you in the right direction.
Please don't PM me or any other members looking for personal assistance. You'll do better by posting (after you've exhausted the search feature, of course) and taking advantage of the collective expertise of the membership instead of a single individual that may or may not be able to help you. Thank you and enjoy your stay at DDB!