|Unless you are or know a linux guru, or are both a hardware and software OS guy, suggestions of building/configuring your own router/firewall is a moot point.|
What I am suggesting is simple to start and can grow with you.
First you need to understand what a vpn is and what it can do for you.
A Virtual Private Network is a secure tunnel thru the insecure Internet that links two network devices together allowing secure communication between them. In your case it would be a laptop to a router [yours does not support vpn clients or links]
Here is an example of what we do in the real world.
I have a Sonicwall firewall router at work and a Linksys wrvs4400n router at home [as examples] of routers that support vpn client access.
The way this works is I take my laptop to a hotel or hotspot that has internet access. I connect to the internet. Then I run the vpn client which then has me authenicate to the router. This is the first set in security.
Next step is I then launch a terminal session [you would use RDP [remote desktop protocol] to then connect to the host pc/server. I am challenged for my network account and password. Once authenicated I am connected to the lan just like I was there in person. But I am sitting somewhere very far away.
You would need to replace your router. The linksys wrvs4400n routers are now below $200 [I paid $375]. You would also need a couple of XP boxes for the users to RDP into. We use 2003 with terminal services which is very expensive for someone in your position. You could just use your 2000 server [you did say server correct? Not workstation] for TS access. Good thing you are on 2000 because 2003 requires you to pay per TS cal [license].
In a simplified version you need;
1. vpn router with vpn client access
2. something in the lan for the remote users to connect to.
Any questions let me know.