yeah, right, I even managed to delete all libqt4 libraries on my N900 (I know, it was definitely a bad idea to run the command on the device...). I have two questions now:

1) libqt4-core seems not to be in any repository, I can't "apt-get install libqt4-core" and "apt-get install libqt4-gui". The latter complains about missing dependency "libqt4-core". I think it was pre-installed on the N900. Where do I get it now?
2) How can I switch the Qt version when running an application? In scratchbox I can compile against 4.5 and 4.6, but when I tried to run the 4.6 application on the N900 it always told me that I can't mix different Qt version. That was why I removed the 4.5 packages, and then the application worked. Is it possible to have 4.5 and 4.6 installed on the device and choose one when running an application?

Peter