I doubt if it's possible. You can't even use JBuilder 4 to use JRE 1.4. There was a hack to have JBuilder 4 use a minor release of Tomcat higher than it shipped with (ie, Tomcat 3.2 instead of 3.1, something like that), and I tried it and found it so sloooow I went back to the version of Tomcat JB4 shipped with. (The apps ran fine when deployed to Tomcat 3.3, though.) Not to sound flip, but the best way to program for Tomcat 4 is to go on eBay and buy JBuilder 6 or 7 (or possibly 5 - not sure about that).