Sony is very good about putting ALL the
drivers needed for all the hardware on their site.
So the
driver for the function keys is there. But depending on the model there can be as many as 40 or more installer files!
It took me all evening to download them all, burn a DVD with them and then install them to restore custom hardware functionality after I also wiped and installed a clean Windows 7. (Of course I left off the bloatware

)
So it's surely on the site if you go to the section for your exact model. The only hard part may be that the
driver will not say "Function Keys
Driver" but will have some compeltely cryptic name like "HWInstaller2"
I would DL everything and install everything but the obvious bloatware. At some point you will find your keys magically start working... (I'm sorry that I don't remember the name of the exact file that got my keys working, but if your laptop was a different model than mine then the driver may be different too)