vpn connection over internet problem

I work in the following simple device configuration
and tried to get a vpn connection over the internet :

desktop pc ___ router ___ internet/WAN ___ router ___ desktop pc
vpn client ------------------------------------------- vpn server


If the client is "windows xp home" and the server is "windows xp professional"
the tunnel and the release of files/folders works perfectly.

If the client is "windows vista home" or "windows 7 home" or even "windows ce 6"
and the server is "windows 7 home" the vpn tunnel gets established but if I enter
\\x.x.x.x ( vpn server ip-address from the details tab of the connection status )
on the client the files or folders released dont appear - only an error message.

If I enter \\x.x.x.x on the server machine the released folders show up correctly.

Is perhaps "windows 7 ultimate" a prerequisite for a vpn server ?

The port 1723 is forwarded. I have a non-DHCP ip-address on the LAN connection
of the server.

Surprise, surprise !

here I want to report at least that with Android 2.3 and 2 free little apps the connection and file sharing with Windows 7 works out of the box :
( a little bit water into the wine : the ease of operation of the two apps should be worked upon in the future )

5 VPN : establishes the VPN tunnel to the remote Windows 7 system over port 1723
AndSMB : connects to the remote VPN Server and indeed shows the shared folders and files ( simply a kind of "net share" list ? ) and lets you download them.

Perhaps this is an alternative way to exchange private/confidential data with partners worldwide... without molesting/benefitting the Kim Dotcoms of the world.

Hope this helps.