Static IP address through W2K VPN

I am trying to configure our company’s VPN server and because of the way our virus updates go out I need to have the remote access clients dialing into our VPN with their individal static IP address. We are using the W2K Remote and Routing Access VPN and it always assigns one of a small group of static ip address. Is there anyway for the remote user to obtain access and still keep his/her ip address? We have tried defining a DHCP reservation but the VPN just ignores them. Any ideas greatly received? Clients are win 98, w2k laptops. Network is NT4.0 domain, VPN is on w2k server outside of firewall. Thks