Slackware :: Qt 4.5 Vs Qt 3.8 (textbook Says Qt 4.3) - "qmake" Does Nothing

Alright dig this, what if I have slack 12.2 and I remove the qt 3.8 (or 3.8.8 or whatever it was) with pkgtool and then I install qt 4.5 or something with a slackbuild. If I do that then the command "qmake" now does nothing. I have to create a file called ".profile" in my home directory and put PATH=/tmp/SBo/qt-x11-opensource-src-4.5.1/bin:$PATH export PATH

in that file, then log out and log back in. Now "qmake" works. So slackbuilds don't do that stuff automatically for me? Or was I supposed to do something with ldconfig or something? now suppose I have a book that teaches QT but it says to use QT 4.3.2 or better. Can I put qt 3.8 back on my system to get konsole and konqueror and all that stuff running again and still use qt 4.5 to compile my own stuff? Or is it possible for my KDE 3 apps to use qt 4.5 instead? (I doubt that.) Can KDevelop 3.5 compile and do stuff with qt 4.5? Or should I just give up and install slackware 13 and use the beta version of kdevelop 4? (I'm not sure I want to use a beta kdevelop.)