For java applets, I use Sun's JRE, J2SE v 1.4.2_04 JRE. There is a Mandrake rpm available to Club members or you can get Sun's rpm here:
http://java.sun.com/j2se/1.4.2/download.html
I think installing the rpm will create the link for Mozilla or you can make your own:
$ ll /usr/lib/mozilla/plugins/
total 1801
-rw-r--r-- 1 root root 856 Mar 22 01:24 flashplayer.xpt
-rwxr-xr-x 1 root root 1614432 Mar 22 01:24 libflashplayer.so*
lrwxrwxrwx 1 root root 67 Apr 18 04:52 libjavaplugin_oji.so -> /usr/java/j2re1.4.2_04/plugin/i386/ns610-gcc32/libjavaplugin_oji.so*
-rwxr-xr-x 1 root root 79864 Feb 12 04:46 nppdf.so*
-rw-r--r-- 1 root root 4139 May 10 2001 raclass.zip
-rwxr-xr-x 1 root root 129360 Mar 4 06:00 rpnp.so*
There are installation instructions at Sun and the link can be made, as root:
ln -s /usr/java/j2re1.4.2_04/plugin/i386/ns610-gcc32/libjavaplugin_oji.so /usr/lib/mozilla/plugins