there are some issues when running openvpn on windows 7, which have mostly to do with windows itself (and its network location awareness / homegroup stuff).
some workarounds exist, but they depend on your exact openvpn setup. Common things to try are:
* add the following to the client config
register-dns
route-method exe
route-delay 5 20
* make sure the tap-win32 adapter is marked 'private', not 'public'
* disable the firewall on the 'tap-win32' interface