First, if you are tight in time, I suggest you go with hosted VPN providers. People mentioned about them in various places in this forum.
Decided to go with your own VPN concentrator? There are 2 types: SSL VPN and IPSec VPN.
SSL VPN: the way it works is just like how http uses SSL (protocol) layer to connect to https enabled web sites except the following:
- In both https and SSL VPN, server sends server certificate but client must have client certificate in SSL VPN case. Some people says this as two way certificates
- HTTPS enabled sites must obtain server certificate from commercial/well-validated/accepted certificate authorities (CA) whereas in SSL VPN case, it is better (and free) if you create your own CA (you need Linux for this purpose; openssl command can do all this for you)
Compared to IPSec, SSL VPN has limitations. Client in SSL VPN case is your web browser as such any application that you want to use over VPN tunnel must go through the browser, meaning that your app and browser must work with each other; this is one big limitation of SSL VPN. Advantage being that it is significantly easier to configure and you don't need dedicated VPN client. If you want to go with this route, check out www.openvpn.org and read stuffs from there.
Here comes IPSec VPN. If you google up OSI Networking Model, you'll see the IP layer in the figure. IPSec (think of it as layer) works with right above (normally) it and sometimes right below it. Advantage: any app that works with your OS will work with IPSec VPN. Disadvantage: a lot of work for configuration/troubleshooting and dedicated VPN client, IPSec client.
In any case, SSL or IPSec, you DO need a firewall that is actually reliable and configurable, meaning (I like to say cheap ass) no consumer SoHo routers. If you decide to go with Cisco VPN 3000 series concentrator, I can help you (client-concentrator scenario) out here.
You do not need static IP addresses but you do need a fixed DNS name. You can get one at www.dyndns.com
if they are all windows xp, you could just enable file and print sharing and keep them in a public folder. you can set up a vpn very easily with windows server. all that ipsec ipsec stands for internet protocol security. its all encryption and forms of encapsulation of data so that people or data sniffers cannot download your information and translate into something that they can use maliciously.