Securing remote connection in Microsoft Windows

I have a virtual server running a Windows Server 2008. I'm connecting to it through Microsoft Remote Connection. Now, this service is generaly avaible to anyone to try and connect to my server providing user name and password. My goal is to secure it so no one could even get access to the service and try to provide user names and passwords.

I tried SSH tunnle (using free sshd server), which is a perfect solution because I disabled the ports of the service, thus allowing the remote connection to work only when connection through the tunnle, and in order to be connected to the tunnle one has to provide user name and RSA public\private key, in addition to the user name and password of the remote connection.

But the SSH tunnle is really not working well, sometimes I'm not able to operate the remote connection and it takes a lot of time to present the desktop.

Is there any other solution?

thanks.