I don't think that you really would want to open your server up to access from any network, which is what adding a 0.0.0.0 network would allow.
All you need to do to allow your VPN user's access is to add their networks into the 'Local Networks' page in the server-manager
The following page will show you where it is (even though this is a screenshot from the beta 6.01 release, it is the same)
http://no.longer.valid/xoopsgallery/view_photo.php?xoops_imageid=126&set_albumName=sme601&id=localnetYou say on a revios post that your Local network is 192.168.2.xxx with subnet of 255.255.255.0
say, for example that your VPN users connect with a 192.168.3.xxx with a subnet of 255.255.255.0 all you need to do is add 192.168.3.0 with the above subnet and the address of the router which joins the networks.
This should then allow your VPN users to access the shares, but this also allows them access to the server-manager if they happen to know the admin password.