First, the DiskStation with the VPN won't have a "virtual IP address." Inside the local network, it will have either a Fixed or Reserved IP address you've assigned in the router, or whatever you're using to serve internal DHCP. The PPTP VPN will be on port 1723 of this address. If you want to access the VPN from outside your local network, you need to port forward in the router from 1723 external to 1723 on the DS, and get yourself a DDNS account, which provides a fully-qualified domain name (FQDN) to your network. You can set this up in the DS or in some routers. All it does is make a connection to the DDNS provider with your DDNS account username and password, and the DDNS server gets your current external IP address from that connection and applies it to your FQDN.
Assuming the Mac is not at this location (why else would you connect it to the DS via the VPN), go into System Preferences -> Network and add a VPN connection. The server address will be your DDNS FQDN. Create a cryptically named admin level account with a robust password on the DS used for this instead of using the admin user and put it in here. I advise you use Maximum encryption (128-bit), but will mention here, PPTP isn't all that secure. Then click Connect.
Once you've connected, the Mac is now inside the local network. In the Finder, select Go -> Connect to Server, enter the IP address of the PPTP range you configured in the DSM, and you should be able to choose shared folders in the resulting menu.. Click on the share you want to use from the DS on the Mac and it will mount, with your DiskStation showing in the left side of Finder windows.
Last edited by myCloud
on Sat Apr 21, 2012 2:31 pm, edited 2 times in total.
DS 1512+ w/3GB, 5 x 3TB Seagate ST3000DM001 8.2TB RAID 6, half files/half Time Machine.
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DSM 4.1-2661 w/SSH + SFTP, VPN Server, Syslog Server, Media Server, Mail Server, Mail Station,
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