but I don't know the way to connect SME Server to Windows Servers...is it possible??
Yes, it's possible, OpenVPN runs under Windows. Just create a OpenVPN server on SME using the Site2site contrib and then install and configure an openvpn client on Windows. You'll have to configure it manually, but it's not that hard. The config file should be something like this (in this example, it's using the TLS auth method, not the shared secret one)
remote sme.domain.tld
port 1195
nobind
dev tun
proto udp
tls-client
ca cacert.pem
cert cert.pem
key key.pem
tls-auth takey.pem 1
route 192.168.10.0 255.255.255.0
ip-win32 dynamic
ifconfig 10.13.0.2 10.13.0.1
comp-lzo adaptive
mtu-test
pull
register-dns
up-delay
keepalive 10 120