1. Download devcon.exe from some Microsoft site. Devcon Overview

2. Open netrasa.inf in c:\windows\inf

3. Look for the section [Msft.NTx86 or MSFT]

4. In the DeviceID column, you can see the installable devices.

5. Run this command to install the WAN Miniport (PPTP):
devcon.exe install c:\windows\inf\netrasa.inf MS_PptpMiniport

6. You can install the other devices similarly. I think you will need MS_L2tpMiniport, MS_PtiMiniport, MS_NdisWanIp, MS_PppoeMiniport additionally

7. If the above doesn't work, try coping a good netrasa.inf  from another server of the same type.