Well, for those who care, I ended up just downloading the kdebase-4.2.3-i486-1.tgz package from a mirror listed on the Slackware site.
This is the version used with KDE 3.2.3... you know, when the 'Application Launcher' WORKED!
I was wrong about the name 'launcher_panelapplet;' rather I copied the two files from the .tgz :
/opt/kde/lib/kd3/run_panelapplet.la
/opt/kde/lib/kd3/run_panelapplet.so
to their corresponding place on my system. Because I'm a noob, after I did such, I gave it a good 'ldconfig.'
On a similar note, I noticed KMix (docked in the system tray) is also, like the 'Application Launcher' applet, biased towards the Windows and Macintosh horizontal panels and does not cooperate with my vertical panel. Clicking on it used to bring up the full audio slider board window. Now it pops up a window similar to that of the master volume control in Windows. This change I don't mind; however, the window is created underneath my panel.
I should also note, my panel hides.
I'm just noting a little haste in the development of some things KDE. Things that used to work but are now a little bit broken in some regards.