> i would like to install ruby 1.9 and qt 4.5 on an windows xp (yes, i
> usually also prefer
> linux, but unfortunately i need this for my job ... ) box, but didn't
> find any sites with
> installation packages (i did succeed installing qt 4.3 for ruby 1.8,
> but this version has some bugs in the qgraphisview module, and i would
> also like to switch to ruby 1.9 in the mid term).

Might be hairy.  The best bet would be to use new mingw version with the devkit.
http://rubyinstaller.org/
http://rubyinstaller.org/downloads/
http://programming-gone-awry.blogspot.com/2009/05/ruby-19-one-click-installer.html
and see if you can get it to compile...I guess.
You could also ask at the ruby installer group.
http://groups.google.com/group/rubyinstaller
GL.
-r