OK it's 2 days later and I still can't get one of the Xboxes I own to download the dashboard update. I've tried all kinds of things like clearing the cache, unplugging my router, unplugging everything that's plugged into the 360, detaching the hdd but nothing has worked. 

When I turn on the 360 for the first time, I get the prompt to do the update then the old style gray box opens with a green download bar that fills up in like 2 seconds. Then the new style white box opens and the green bar gets about 3/4 full and it stops and a message comes up about how it can't process blah blah blah then some big status code. When I try to do it again after that, I get the old style gray box again but this time the bar only fills about 3/4 and it stops. I then get an update failed message and it tells me the steps to test my connection. When I go to test my connection it gets to the last stage and then it starts the loop of prompting me to do the update all over again.

I had this problem on the 1st with my other 360 but I got it to work later in the day and haven't had any problems with it since. So I'm looking for some suggestions before I make the dreaded and most likely useless 1-800 call. And when I say suggestions I don't mean things like "get a PS3" or "stop taking it up the ass from MS" and so on. Thanks. 

Try moving your hard drive from one Xbox to the other and see what happens.

For the Xbox with the HDD that has the update, make sure you can connect to Live.

For the Xbox with the HDD that doesn't have the update, see if it lets you update it.

Awesome idea dude, thanks a lot for now I have a spark of hope. Only thing I'm a little worried about is that I've had issues in the past with this HDD. It was one of those situations where it wasn't working at all for a while, I would keep getting some error code. Then it started to work out of the blue. There was a time after that where I removed it for some reason I can't remember now, and I had the same error code problem again. Once I got it to work after that I vowed never to mess with it again......until last night that is. At least it didn't happen this time but I'm desperate here and it's worth the risk to try your idea. It's pretty much useless to me without the update. Thanks again.

USB flash drive plus  http://support.xbox.com/en-us/pages/xbox-360/how-to/update-xbox-360/system-updates.aspx

You just taught me something. I never knew you could install the updates from flash drive or CD/DVD.

You are the man! Thank you again, sooooo much.