Windows XP mode supports USB 1.1, and what is the USB number of your ADSL?
You can try on 7 :
1. Right-click the driver setup file -> properties -> compatibility tab -> xp compatible. See if it installs.
2. Extract the driver to a hard drive folder. Then devices manager -> right click the modem -> update the driver -> browse to the folder with the driver extracted.
Finally, this may work:
3. Devices manager -> right click the modem -> update the driver -> select microsoft generic driver from the list (if it's on the list).