Eclipse 3.x and subsequently MyEclipse 3.x requires a JDK 1.4 or greater to run. Also debugging requires JSR 45 spec be supported by the application server, I don’t think WebLogic 6.x supports that, but besides that a 1.4 VM is required as part of that debugging using that spec as well… so right now with that old of a version of WebLogic and using a 1.3 VM you are in a ‘worst case’ situation as far as debugging is concerned.
Are you able to developer with 1.4 but turn on 1.3 compliance and work around the limitation that way?