I also have the problem and it is because of VMware's network adapters. As I see it, there are two solutions:
- Disable the adapters altogether and use bridging instead (in VMware, select edit>Virtual network settings and disable the adapters), as explained here.
- Apply this hack.
I don't understand why VMware still didn't fix the issue. There may be other reasons why Vista deactivates network discovery though, but VMware is certainly one of them.