Make aplugins folder in your profile and install it in there.
ln -s /path/to/j2re1.4.2_03/plugin/i386/ns610-gcc32/libjavaplugin_oji.so
Change /path/to in that last line to the real place where you installed java. Also, if you installed a slightly different version to me some of the folders may have different names on your machine. Get it right or the symbolic link will be pointing at the wrong place and so won't work.
As megaspaz said, it must be the libjavaplugin_oji.so in the ns610-gcc32 folder.