My team is moving from Visual SourceSafe to Subversion soon, while developing/supporting a legacy project in Visual Basic 6.0, so I have a couple of questions:
Since Subversion uses an update/edit/commit cycle (rather than checkin/checkout), you will need to be especially careful with binary files. Most forms in VB6 consist of two files: MyForm.frm and MyForm.frx. The *.frx files are binary, and thus cannot be merged.
Given that, I would set up Subversion to require "locking" on .frx files. This means that only one person can check the file out at a time. By doing so, you will enforce that only one developer can modify these files at a time, and it is always clear who that person currently is. If you don't do this, you are setting yourself up for some major headaches.