Networks

i have a odd network setup and my boss is too cheap to buy anything and i'm needing VPN to make life easier i'm not able to put my VPN router on the outside of my sbs2003 server because the connection is over 300 feet and going through 2 switches so once i connect a router it just blinks and wont connect to anything and i can only hook one through the internal network from the private NIC of my dual NIC sbs server i'm able to forward the tcp ports i need for pptp but not the GRE protocol is it possible to do at all or does anyone know of another solution ? i put the VPN server by the internet connection on the 1st floor and was able to get connections but could not route it to my internal network from the small business server i've been pecking away on this for 3 weeks and i'm at my wits end any help or advice would be apprectiated

the problem with connecting it downstairs is he shares an internet connection with another company and they use 192.168.1.x then it goes to the upstairs and the sbs server supplies the office with 10.0.0.x through a dual nic setup