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 loosing 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 an capture it's output.
But for things like GUI changes and debugging there is really no choice but to revert back to the VB6 IDE.
Here is 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
FWIW 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 an capture the output.