Note to above: I couldn't extract the 32-bit 1.4.2 from Sun's site either (from www.java.com) - you have to get 1.5.0 from www.sun.com for this trick to work.
AWESOME! It worked. I was copying the plugin before rather than linking it. Also, I'd renamed the directory to sun-jre-1.5.0... one of these must have been the problem. Thanks a bunch!
something else I noticed: if you install another jdk/jre in addition (i.e. have a 64 bit blackdown and 32 bit sun java for firefox-bin 32 bit), the symlink to the plugin disappears when you install that other jdk/jre