Extending wireless network w/o ethernet

Thank you for your patience and your detailed instructions.  I know you're trying to make them foolproof, but I seem to be countering them.  I tried a number of different things unsuccessfully, but I think it would be better to document what happened when I tried to follow your precise steps:

Steps:
1. Changed the settings on the 3800HGV.

2. Plugged in the DLink router via a LAN port.

3. (Assume you're talking about the desktop connected via ethernet to the 3800HGV.)  Went to Local Area Connection Properties, chose Internet Protocol Version 4 (TCP/IPv4).  Made the changes, rebooted the desktop. 

4. After rebooting the desktop (running Windows Vista FWIW), opened Chrome browser and tried to go to 192.168.0.1.  Wasn't able to connect.  ("The web page at http://192.168.0.1/ might be temporarily down or it may have moved permanently to a new web address.)

So that is where I got stuck.  Some observations that may or may not be important:
1. I pressed the reset button on the DLink router before trying this, so I assume it's on factory settings.  If not, should I connect a computer directly to the DLink router via ethernet?  I have a laptop on the 2nd floor, so it wouldn't be a problem.  If I do this, though, I'd need to know when to have the DLink router connected to the Motorola box and when to have it completely unconnected.

2. When I look here on the 3800HGV: http://192.168.1.254/xslt?PAGE=C_2_0, I see that the Private Network DHCP range is 192.168.1.64-192.168.1.253.  So the IP address that's supposed to be assigned in step 4 would be out of that range.  I'm not sure if that's important.

I'm sorry for all of this. Prior to this experience, I considered myself very much computer literate, but this is causing me to rethink.

This is exactly what I had to do.  Once you start making changes to your router and plug it into the RG, you are unable to log back into it and make other changes.  I had to do a factory reset and make all the router changes before plugging it back into the RG.  I also found it's easier to plug your laptop directly into the router and then directly into the RG to make changes.  After everything is done, plug the router into the RG and then connect your laptop wirelessly.

Also, don't forget to write all this down somewhere you won't lose it.  Chances are you'll need it later and won't remember what you did.

First, the good news:  I think it works.  Thanks so much for all the help!

Some lingering thoughts on this, perhaps to help others who try to do this:

1. When I configured the DLink router, I had to do the factory reset, log into 192.168.0.1 and then change the settings according to your directions (give static IP of 192.168.1.10, the 255 submask, and the 192.168.0.1 gateway, disabled DHCP).  (I also had to choose DNS settings, and I used 8.8.8.8 and 8.8.4.4.)  The first concern I had was that after I made these configuration changes and rebooted (with the router connected to nothing but my laptop via Ethernet), I still logged on to the router by pointing to 192.168.0.1.  I was expecting that I would now be pointing to 192.168.1.10, but that didn't work. 

2. I then plugged in the Dlink router to the Motorola box on the 2nd floor and rebooted the HGV3800 in the basement.  I'm not sure if I needed to do the reboot or not.  After I the HGV3800 was back up, I went on the desktop (connected via Ethernet to the HGV3800) and pointed the browser to 192.168.1.10.  Nothing.  Then tried 192.168.0.1.  Still nothing.  At this point, I just assumed that things were still broken.

3.  I then looked at the home page of the HGV3800 (192.168.1.254) to see the list of devices connected - no listing for 192.168.1.10, so I was certain it didn't work.

4. Went back to the 2nd Floor Dlink router with my laptop and plugged the laptop in via Ethernet (with wifi disabled).  It actually got an internet connection, which was good news.  Even better, when I pointed the laptop browser to 192.168.1.254, I got the home page for the HGV3800, so at least something seemed to be going right. 

5.  I then unplugged the laptop from the Ethernet connection, disabled the wireless on the HGV3800 and turned on the laptop wifi (so that the only possible wireless network available would be coming from the 2nd floor Dlink router), and it actually connected.

I did not go through the steps of temporarily changing the desktop's settings to 192.168.0.10, then changing it back, but that doesn't seem to have affected anything.  I guess the only disappointment is that there doesn't seem to be any way at all (either by direct physical connection or through the network) to change the settings of the 2nd floor Dlink - it seems that I'll have to do full reset if I want to change anything.

But that's a minor gripe and overall, assuming this continues to work, I'm thrilled and grateful for everyone's help.

My experience is basically the same.  After I made the changes to my router and plugged it into the RG, I was no longer able to log into it to make any subsequent changes.  If I ever need to change anything, I will need to unplug it from the RG and do a factory reset of my router.