I have an mp4 file on my laptop that I'd like to view on my Xbox. I'm unable to connect via Windows Media Player (due to administrative reasons, something I can't change), so the only real way I can think to get it to the Xbox is to transfer via portable HD or USB stick.
I tried this last night, but when I plug the USB portable HD into the USB port, my Xbox sees it as a storage device that it wants to format.
Is this the right to eventually move the mp4 over to my Xbox to watch?
You need to format the USB drive using FAT32. The current Xbox 360 software can see at most 32 GB of the drive. You may need to use the XBox to format the drive. Personally, I just used a 16GB USB stick, and for most purposes FAT32 is sufficient (for movies smaller than 4GB).
There's a neat trick for big movies: format the USB stick using a *Macintosh* (HFS+ format). No joke.
It turns out that this allows the Xbox 360 to read AVI files bigger than 4GB. I've played an 11 GB movie off a USB stick in my Xbox 360 this way.