Apple Mobile Device Support comes from the iTunes download. You could also search the Apple KB area in support to see if there is an alternative place to get it at.
As far as the other poster's comment with 3.0, I have two iPhones, one first generation and a 3G and neither have experienced a single issue since upgrading both of them to 3.0
Well, you can go into Control Panel and remove it and see if a fresh install of iTunes will fix it. Other than that, my only other recommendation would be as I said before to search the Apple KB to see if there is an alternate way to get the file.