Bear in mind that I admin a lot of RH9 servers but don't use Java myself and have never tried to install it. Thought I'd take a stab at it just for the heck of it though...
http://java.sun.com/j2se/1.4.2/download.html seems to be the place to be, small amount of surfing their site to find the download page. Downloaded the Linux JRE rpm "bin" file. Odd, it's not an RPM, it's a binary file you run that extracts an RPM file. Makes you agree to the license agreement so that's why they do that. No big deal...
# chmod a+rx j2re-1_4_2-linux-i586-rpm.bin
# ./j2re-1_4_2-linux-i586-rpm.bin
# rpm -ivh j2re-1_4_2-linux-i586.rpm
# java -version
At this point it still shows the installed RH9 Java stuff, whatever it is... So
# rpm -ql j2re-1.4.2-fcs
Shows me all the stuff from that Sun JRE RPM went into /usr/java/j2re1.4.2 In there is a bin directory with a java executable in it.
# /usr/java/j2re1.4.2/bin/java -version
That looks like it... OK, so this /usr/java/j2re1.4.2/bin directory is new and is NOT in my path... I'm logged in as root so:
# vi /root/.bash_profile
This line:
PATH=$PATH:$HOME/bin
I changed to:
PATH=$HOME/bin:/usr/java/j2re1.4.2/bin/:$PATH
Previously it took the contents of the environment variable $PATH and set it equal to itself and $HOME/bin appended to it. I changed it to make the PATH $HOME/bin, then the java bin directory, and then the rest of whatever itself was already set to. Logged out and back in and java -version now gives what I expect.
Potential problems with this way of modifying the path is that running things from cron or 'at' jobs or automated scripts might still use the default path and not find the Sun 1.4.2 Java files. Probably /etc/profile would need to be appropriately modified to set the correct PATH or make sure to give the full path in any scripts or cron jobs or whatever to the executable you want. Many other ways to skin this cat, that's just a couple.
Good luck!