Assigning Static IP to a computer in a LAN (in Windows 7 home basic)

I have some confusion Plzz help me to clear as don’t know much about networking..

I want to access a web application on computer that is part of a private network. The network has 15 to 20 comps having Ip’s of range 192.168.1.xx.

I want to assign a static ip address provided by my ISP(Internet Service Provider), to the computer hosting my web application so that i can access my web app. from any where using a internet connection.

Please let me know wats the procedure.

Ashish