VPN thru MS proxy server w/ Mac clients

I have a DSL/ISDN WAN with Internet access thru a MS Back office server. My boss has a Macintosh LAN at home along with 512k DSL and wants to get remote access to a Macintosh LAN at one of our sites over the Internet thru our proxy server. I installed Routing and Remote Access Services on the NT server and added PPTP packet filters to the proxy services. I use static IP addresses on all of the WAN workstations (because we have medical equipment that doesn?t support DHCP) but my boss doesn?t have a registered address. I think if I was working with PCs I could just install MS VPN adapter and tunnel into my LAN but I don?t know if there is anything similar for a Mac. As a matter of fact I don?t know much about Macs at all. Thanks in advance for any guidance.