Do ADSL Modem / Routers need special drivers installed on Windows 7?
No! Cable and DSL modems and routers are network devices. If your computer is communicating with your network (in other words, if your NIC is working fine) then that's all you need.
Now if you are not connecting to the Internet, there may be a setting blocking you, but that has nothing to do with drivers. Understand you MUST connect to your network first, BEFORE you can connect to the Internet. And your network consists of everything on your side of your "gateway" device (the modem) - even if only a network of one computer.
Sadly, many network device makers and suppliers (most notably ISPs that provide modems) will often include a "utilities" disk or setup "wizard" disk to help you connect. That would be good if that is all they did but very often they also foist all kinds of unwanted junk on your system - therefore, I NEVER, as in NEVER EVER use the supplied disk, and instead, setup networking from within Windows only.