I had to get an OpenVPN install working on my boss's Vista PC. I know, I know, but I can't convince him to get a Mac and run Parallels.
It mostly worked, in that the client connected to our gateway server, but traffic wouldn't go between his machine and our LAN. Then I found this article, which boiled down these steps:
Add to your .ovpn file the following two lines:
route-method exe
route-delay 2
Then reconnect, and everything works.
