There is a PDF guide for setting up email using WinGate 5.x availible here
http://www.wingate.com/files/Mail_Serve ... narios.pdf you would be using scenario 3. The guide steps you through the setup and includes screen shots etc.
Probably the best thing to do is work your way through that and if you have any issues then we can take it from there.
I recommend that you upgrade to the latest version (6.2.2) because it is very stable, and you can get all of the bug fixes and driver upgrades for free. It also has a lot of new features that you can try by activating a free 30 day trial license during the installation. If you decide that you don't need the new features then you can continue to run the latest version with your existing version 5 license.
Yopu can download the latest version here:
http://www.wingate.com/download.php