The DigiNet.inf file is now installed to your C drive with ProTools. It is located at C: Program Files/Common Files/Digidesign/DAE/Controllers
So, simply substitute step #5 by going to this location on your hard drive instead of using the CDROM as the manual specifies.

The complete set of instructions are:

Ethernet control surface installation for Windows systems:
1. Go to the Start Menu, right-click the My Network Places icon, and then choose Properties.
2. Right-click on the relevant Local Area Connection, and then choose Properties.
3. Click on Install, select "Protocol" and click the "Add" button.
4. Click on Have Disk.
5. Point to the DigiNet.inf file in Program Files/Common Files/Digidesign/DAE/Controllers directory on your Local Disk.
6. Follow instructions on-screen to complete the installation.
7. Restart.