There are two types of files available. You want the latest qt-embedded-s60-opensourceYYYYMMDD-4.6.0-tp1.exe file. The other qt-embedded-s60-opensource-src-4.6.0-tp1.zip is the source package used to create the latest .exe and can mostly be ignored. The .exe contains a Windows Installer as shown below, and here is instructions on how to use it.
There are three Qt .sis files included in the .exe. Most of you (unless you work at Nokia and have an RnD phone) wants to install the qt_for_s60_selfsigned.sis together with the fluidlauncher.sis or whatever application you're creating yourself.
Works for S60 3.1, 3.2 and 5.0. If you're using some funky internal RnD SDK, it might work (Hint: use the the "Choose additional folder(s)" option if you're SDK is not in devices.xml).
The code we're building from is whatever is HEAD of http://qt.gitorious.org/qt/qt/commits/4.6. In other words if we break the build, no binaries for that day - oh well. At the moment QtScript and QtWekbit are still not there - but soon my friends, soooon.
Update: As of 2009.09.29 the snapshots contains QtScript and QtWekbit as well. Yay we're so great!. Update2: Well, we're not that great it seems. The .dlls gets copied to your epoc32, but they're not inlucded in the Qt_libs sis files. Fixed now, should be correct in tomorrows snapshots. Update3: Yepp - was fixed today :D.
Final disclaimer: This is not product quality software. It might make your phone depressed and make kittens cry. Use at your own risk.