which mozilla plugin directory? give the full path of the mozilla plugins directory you used.
also which parent directory of the java plugin did you use? are you using the sdk or the jre and what version of java? was java plugin directory path like /usr/java/..../..../ns610-gcc322? if not then you're using the wrong java plugin for moz 1.5.
also, do you have java enabled in the moz preferences?
but anyway need the info.