Could be due to the keyboard using the default Windows keyboard driver, that and as far as a Logitech driver goes it uses the older iTouch which isn't supported under Windows 7. There is one thing you can try and that is Setpoint, Download SetPoint 4.80 - FileHippo.com
and see if it will recognize and work with your keyboard. If it does that should get your volume keys working, as well as allowing you to use the rest of the extra function keys that may not be working.
The above is for the previous version (4.8) as the latest (6.0) has a tendency to be buggy even on mice and keyboards that support it. It is also for the 32 bit version and if you need the 64 bit version, let me know and I can upload it for you.