I've downloaded the latest Skyrim update, then the dragonborn dlc. My hard drive says I have dragonborn installed, but when i look in the add-ons section of Skyrim, it doesnt show up. Any idea why? I really hope I didn't lose $20 on this. Thanks.

Delete the dlc from your hdd then go to your purchase history and re download it, or just go back to the marketplace and dl it from there.

Yes, do this. Happened to me too, this fixed it.

Also be sure to clear the cache on your hard drive after you delete, then re-download.

Try to restart the game. The "loading add ons" message will be extended if done right, and you can play dragonborn.

I am also having problems with the expansion. I dont have a wireless internet connection here so i went over to a friend's house and brought my xbox and hard drivejust so i could play the new expansion. After all that trouble, i got the thing downloaded... and when I get home the expansion doesnt work?? what gives?

Did you also download the new 1.8 patch??

Did you bring your box or just your hdd. If so you don't have the proper license for it to play on your box offline. Just bring your box to a friends and do a license transfer it should be good to go then

Absolutely.
It prepares Skyrim for the Dragonborn DLC.
Patch 1.8 contained files with the info about Dragonborn that people speculated about pre-release.