Logon to Win2K domain thru Linux firewal

I am planning on setting up a nice little Linux box to take the place of a Netopia router our DSL provider supplied at install. We use a Win2K domain here, and I was thinking of setting up a VPN server to log on to the domain and allow access through the broadband connections my users have at home. I figured if I could get a Linux server to handle the VPN logons, everything would be more secure. I’m just not sure how I should go about setting this up. Any help would be greatly appreciated. Thanks!