I have the same problem as huno, I think. I downloaded flash from macromedia.com/shockwave/download, and followed the instructions. My mozilla directory is /usr/local/mozilla, as megaspaz said I got it from mozilla.org. I verified this by right-clicking on the mozilla button on my kde desktop and looking at properties, and it says the command is /usr/local/mozilla/mozilla.
After reading megaspaz's advise, I looked in my plugins directory and found:
]# cd /usr/local/mozilla/plugins
[root@localhost plugins]# ls -l
-rwxr-xr-x 1 root root 856 Mar 14 08:02 flashplayer.xpt
-rwxr-xr-x 1 root root 1470464 Mar 14 08:02 libflashplayer.so
-rwxrwxrwx 1 root root 21056 Jan 13 14:10 libnullplugin.so
So when I installed, I got a .xpt file but not a .class file. I looked in the tarball directory and didn't find it there, either . . . .
[root@localhost plugins]# cd /root/install_flash_player_6_linux
[root@localhost install_flash_player_6_linux]# ls -l
-rwxrwxr-x 1 dale dale 23579 Feb 24 2003 flashplayer-installer
-rw-rw-r-- 1 dale dale 856 Feb 24 2003 flashplayer.xpt
-rwxrwxr-x 1 dale dale 1470464 Feb 24 2003 libflashplayer.so
-rw-rw-r-- 1 dale dale 20728 Feb 28 2003 readme.htm
-rw-rw-r-- 1 dale dale 11301 Feb 28 2003 readme.txt
I tried the install twice. Any advice very much appreciated!