Frank Kromann applied some patches yesterday to the PECL sources of the uploadprogress extension to make it compile under Windows (almost the same as by SteveH provided in a comment of my post yesterday). Therefore, thanks to the pecl4win site, a compiled dll is now already available. Get it here (untested by me..)

He also mentions some documentation that was asked about concerning the package (and the patches), but notes that he "can't promise anything any time soon".