VPN from home to work

I have a XP at home, a RedHat 9 as router and firewall, and a Domain Controller with Windows 2000 Server. On it, i have 2 LAN adapters, one is configured as DHCP server, WINS server for entire network, and the second is not used.
I want to connect from home, and also from some other locations to the domain at work, passing the linux firewall.
What should i do?