If the option to assign a static IP address is disabled for your VPN connections, then you may need to change some settings on your Windows 2003 Server. Here are some steps that you can follow to enable the option:
1. Open the Routing and Remote Access console on your Windows 2003 Server.
2. Navigate to the IP Routing node, and then to the General node.
3. Right-click on the General node and select Properties from the context menu.
4. Select the option to "Enable IP routing" and then click OK.
5. Right-click on the IP Address Pool that you want to use for your VPN connections, and select Properties from the context menu.
6. In the Properties window, select the option to "Enable IP address assignment via DHCP" and click OK.
After you have made these changes, you should be able to assign static IP addresses to your VPN users by following the steps I provided earlier:
1. Open the Active Directory Users and Computers console on your Windows 2003 Server.
2. Navigate to the user account that you want to assign a static IP address to.
3. Right-click on the user account and select Properties from the context menu.
4. Select the Dial-in tab, and then select Assign a Static IP Address.
5. Enter the IP address that you want to assign to the user, and then click Apply to save the changes.
Remember, the IP address you specify for your VPN users must be within the range of IP addresses that you configured in the IP Address Pool.