Microsoft digital signature: how important is it?

Just wondering how important it is to have a "Microsoft Digital Signature". I was going to update my (intel) network card drivers to version 5.1.3, and it warned me about no signature. Alienware lists 5.0.3 on there support site, so maybe those are the most recent with a signature?

I'd just downloaded Intel network drivers from windowsupdate.microsoft.com (with driver dates not as recent as 5.1.3's). Should I wait for the next windowsupdate listed drivers, or install Intel's latest?

My OS is Win2000.

The digital signature just means that it has been tested by Microsoft and has been shown to work correctly. It you trust the hardware manufacturer to release good drivers then install it. Many drivers never get signed as they do not contain vital updates and it is deemed "not worth it." Is there a reason that you are upgrading the driver? It it doesn't offer anything beneficial, and your current driver is working, I'd leave it be.