If you need a true VPN, you will need a VPN router. I assume your WinVista and OS/X are on two separate networks not physically near each other, is that right?
A
VPN router is all you need. Then you configure it with OS/X in the Network settings. You'll likely need a Group Name, the server address (public IP address of the VPN router which you can get from your ISP), account name and a
strong password. Then you're all set to connect using a VPN. What you do with it from there is up to you. I mentioned that I use a VPN to connect from home to my office using an
Adaptive Security Appliance 5510 Cisco router and then use the
Microsoft RDC app for OS/X to connect to any of my servers or desktop PC.
What is your goal for a VPN, or are you just curious to do one?
Edit: Additionally, if you want to learn everything there is to know about VPN's go to Steve Gibson's website and check out the
Security Now podcast. You'll want to listen to episodes 14-19 which are all about VPN's. You'll have to scroll all the way to the bottom. If you end up liking the show, you can also get the show in video and audio via iTunes. but these VPN episodes are older (still relevant as this technology hasn't changed) and are not in iTunes. So you'll have to download these from the
GRC website.