Is it risky to install unsigned drivers if Windows recomends them?  

Hello JL. Hope you survived Irene without any problems.

It should be OK to install an unsigned driver if Microsoft/Windows recommends it. But at a minimum it's a good idea to create a Restore Point prior to the installation. (A system image would be even better.) Then if you have any issues you can roll back your machine.

System Restore Point - Create

Glad to hear you made it OK. I still have relatives on Long Island and they got hit harder than the City. Just some additonal info you might find interesting.

A signed driver is basically a digitally signed driver, which means that the driver software is associated with a digital certificate that allows identification of the publisher of the driver. It also ensures that the driver has never been modified by anyone else, as that would corrupt the signed status and make it unsigned.

So using a signed driver will ensure that Windows can automatically install the driver and prevents malicious software to be installed along with the driver. Considering that drivers operate at a very high security level in the operating system, it is very important to use safe drivers.

Windows Vista, Windows 2008 server and Windows 7 already enforce unsigned drivers to be installed using administrator level access, but how can you know for sure that an unsigned driver is safe?

Well, you cannot really. So always make sure that your security software is up to date and active, and make a backup or create a system restore point before you make any changes to your system.

Source

From what I can gather, Microsoft doesn't go out and solicit software manufacturers to "sign" their product. It's up to the individual manufacturers to go to Microsoft and ask to get a signature. Some software maufacturers (like spyware, viruses, etc) obviously won't seek that signature. But some reputable companies may have too many to take the time to get signatures on every one. Or the software changes so frequently (updates) it wouldn't be cost or time effective.

pooch said:

I may be wrong but believe that the manufacturers have to pay Microsoft for the pleasure, it's hardly surprising that some do not or cannot afford to do it.

Doesn't surprise me in the least Micro$oft might try to make money some how, some way.