VPN or access to office net from home

[semeteyo]

Can Anyone help.

I am trying to access my office network from home. I have the alcatel speedtouch pro adsl modem which connects to the internet. I then have a PC running winproxy which is my firewall, antivirus etc on my network. All pc's on the lan access the internet through that machine. It has two nics, one for the lan side an one for the wan side. The wan side nic is connected to the speedtouch pro adsl modem. The thing is that modem does dhcp so the wan nic gets an ip address. My isp does not provide static ip on adsl. Is there a solution to go in from home to the office PC.

Thanks