I did it this way and it worked
1. find a website hosting slackware-current
2. browse to the directory kde
3. Pop open a termial
4. run the following command
5. Download the contents of kde (the one on the website) into the directory /usr/src/kde (in your computer)
6. run the following command
7. then run the following command
exactly as I wrote it with the *
that will upgrade everything ending with .tgz
after doing that
8. There are also three additional lib files that you will need to install or else KDE 3.4 won't work.
After you install the upgrades with upgradepkg,
8.a. from a terminal, run
8.b. Then look in the error message to see which lib file it can't find
8.c. then go to http://slackware.com/pb/
and download and install that file.
8.d. go back to 8.a. and repeat the sequence till it works.
You will have to do that 3 times.
Note: at that website, search for the lib%$#@, whatever it is called (The file you need doesn't have the exact same name, download the closest one)
Goog luck !