I am stuck at this point, 3 days attempting to configure the VPN connection but failed.

Here is the scenario:

PLDT ISP==>PLDT Modem with 1 static IP address==>BEFSX41 LinkSys Router==>D-link switch==>5 computers.

At this scenario internet connectivity is okay. But configuring VPN is not yet okay. The objective of the VPN is my boss who is now in the US, using his laptop wants to connect to our office here in Cebu.

Questions:
1. We have one static IP address in the office class 124.xxx.xxx.xx. How to configure inorder for me to assigned this static IP address to one of the 5 PCs?
2. This VPN router supports IPSec, PPTP and L2TP passthrough (this can be seen under Security, VPN, VPN Passthrough, options there to Disable and Enable IPSec, PPTP, L2TP). How do I configure using one of this VPN passthrough?
3. Any suggestions to become this VPN configuration possible? What are the lacking components or other requirements?

Thanks in advance, mga bro.