I had the same problem that another reader mentioned where Java 1.4.2 would not show on the software update, or would not install asking for the 1.4.1 update, etc. In my case, doing a finder search for all files containing the term softwareupdate (which included preference files, etc.) and deleting them, resolved the problem. Apparently resetting software update files was necessary. After that Java 1.4.2 installed fine.
A common OS X theme unfortunately -- when problems occur search on words and delete pref files. Another pref problem test is switching users. The good news is the UNIX naming conventions and OS X file organization helps with finding things. Also, OS X find is super fast. Bad news is the recurrent issue with bad prefs.