QT3/QT4 Coexisting

How are you folks getting QT3 and QT4 to coexist together and to ensure KDE4 finds QT4 and not QT3 and 3.5.10 or Trinity find QT3 and not QT4? I'm looking at the latest Slackware release. Looks like the QT4 location is defined by the QT4DIR environment variable and not QTDIR. That is good news. Another difference is in the KDE3 days, QTDIR pointed to /usr/lib/qt, which was a sym link to /usr/lib/qt-3.3.8b. In the latest Slackware release, the QT4 files are installed directly to /usr/lib/qt and there is no sym link. If I understand correctly, when I build a QT3 package on a QT4 system, I should compile QT3 to install at /usr/lib/qt3 and then set a QTDIR environment variable to that location before compiling 3.5.10/Trinity packages. Does this sound correct? Darrell