OK, I successfully build all qt4 packages in scratchbox and I have now ARMEL binaries for libqt4-dev - qmake/moc/uic/etc. It took a couple of hours, so in N900 it would take a couple of days I guess.

Let's see can it work for simple qt4-based application build in N900 (I target googlelatitude) now. If it work I can share that binaries.

EDIT: googlelatitude build on N900 works... some issue does exist but it may be bugs...

In any case - big thank to daperl for providing clues and build bugs fixes.