When I do Option + Restore in iTunes, it does bring the file menu up. I browse to the file I downloaded, but I won't let me select the folder. It will let me select individual files in the folder, but I don't think those are what I want.
From what I have read in the posts on here, it is available through iTunes, if you are running the latest version of iTunes (7.5). It seems that most people that are looking for the update, have not updated iTunes, and thereforee do not see the latest firmware.
It is also entirely possible that since this version was already hacked the day before release, that Apple is not pushing it out till the can patch it.
I cannot confirm either myself, only go by what I have read here.
I personally downloaded it manually, and it installed easily with no problems.
The really nice thing is that if you have to restore, it saves EVERYTHING now. Your passwords for email, VPN and WiFi, your Notes(which has been happening sice at least 1.1.1) your Pics on the camera roll, etc. Plus, it syncs and restores a little faster now as well. it was restoring my music a little faster than a song a second.