Because the VB6 IDE does not detect file changes made outside of the IDE, it can be quite difficult to develop code outside of the VB6 IDE, without running the risk of losing code changes.
But it is possible to run a VB6 project build from the command line, so it is possible to do simple VB development using any text editor/IDE capable of running a command and capture its output.
But for things like GUI changes and debugging there isn't really any choice but to revert back to the VB6 IDE.
Here are the commands needed to run the build from the DOS prompt:
set PATH="d:\Program Files\Microsoft Visual Studio\VB98\";%PATH%
vb6.exe /out ErrorFile.txt /make MyProject.vbp
For what it's worth, the Zeus IDE has the ability to import a VB project file and display the project details into project/workspace tree. It will also run the build and capture the output.