Hi, you will have to give some info about the modem, as the exact model. Is it connected to the computer through an USB, or an Ethernet port? Do you need any special software to make it work using another os?
Most of the time, you have to open a browser, type http://192.168
.1.1 in the address bar, a screen asking user / password appears, admin / admin are usually the defaults, then you get the modem settings page, and you have to configure your internet connection using the data provided by your ISP.