Ok, so I'm brand new to macs this week.

So far I love it.  I need some help on VPNs though.  There are lots of you knowledgeable types on here who might be willing to help me, so I'm asking before I give up.  

I was given a brand new iMac to do my job from home.  There are three of us working together, all in different home offices in different locations around the U.S. and we need a way to all have access to the same files.  I have been given the task of making that happen.  I read that the OSX I have on here is perfectly capable of performing as a server version for less than 10 users at a time as long as I went through the steps to enable those capabilities manually or run a program like iVPN.  I decided to give iVPN a try.  I gave the mac a static assigned address on my LAN and told my router to pass connections on TCP port 1723 and UDP ports 1701, 4500 and 500 to that address.  I created three users in iVPN and made sure connecting users would be assigned addresses that would never conflict with assignments from my router to computers on my LAN.  I asked someone who is running Vista on their machine in another state to give it a try before I announced I'd done it.  She was able to log in just fine.  When my father (my boss, lol) tried it he couldn't connect.  He's on a Mac too.  Any thoughts, or am I an idiot who just needs to pay a professional to figure this out for us?