That's what I ended up going with, mrogers. The guide is now updated for AT&T customers on Windows.

dakidgo, you should be fine to proceed now. Let me know if anything doesn't work.
That is one caveat that I just noticed, as you mentioned it. It appears the drama surrounding NateTrue's premature release was a bit justified, then. I had assumed that the ringtone fix in the final step also fixed the problems with music, but I guess I was wrong. This is where the "you're responsible for any changes you make to your phone" provision comes in.
Ringtones do work with the fix off Installer.app, though, and I haven't encountered the carrier problem.
This works fine on phones that are 1.1.2 out of the box (such as mine). The only thing you cannot do, however, is downgrade your baseband now. You're also fine restoring the back up off of iTunes, it won't mess with your jailbreak.
The source on rapidshare does not matter, and the "chmod" line handles the problem with it not being executable.
Some applications that relied on the way things were done in 1.1.1 and 1.1.2 will not work, no (such as Summerboard). As always, you are jailbreaking your phone right after the jailbreak was released - a risky thing. However, there is nothing inherent that makes 3rd party apps in general not work, and Summerboard is the only app so far that I've run into that doesn't work on 1.1.3. Updates for these apps will be out soon enough.