I never managed to get v5 running in VirtualBox (it refused to create directories), but now I tried b7, and it worked! Great news:-)
Solaris (OpenIndiana 148) + VirtualBox 4.0.4 + Win7 Enterprise 64 + Newsbin 6b7
The GUI is a bit laggy (which is probably to be expected considering that I run it over X tunneled over SSH from the Solaris server, displaying on my OpenBSD work station:-))
Sometimes it hangs (the GUI), but it seems to be related to running low on memory; apparently I need to go from 8 GB to 16 GB on the server...
- mho