Advice direct from Microsoft is to either:

Disable driver signature enforcement

or

Test-sign your driver using a certificate you create on your machine.

Here’s the link to that advice:

http://answers.microsoft.com/en-us/windows/forum/windows_7-windows_update/windows-7-64bit-update-unsigned-drivers/fd05a6f5-217a-e011-9b4b-68b599b31bf5

Until Windows 7 will behave itself when running drivers that are not digitally signed by Microsoft the above is a workaround. If a user feels that security is lessened by using either or both of these methods they can always beef up security by adding an application white-listing component such as Secrue APlus (No AV version):

https://secureaplus.secureage.com/Main/release.php

It can be set to either warn or block if an unsigned file attempts to run although I suspect that the average user will struggle to configure the program to get the best use from it.

Microsoft’s policy to allow only signed drivers to be loaded by the OS can be considered an extra safety measure that aims to make your system a bit more secure and prevent malicious code from execution. However if you wish to install software when the manufacturer has not obtained digital signatures then you options are either:

Don’t use the software

or

Use one of the suggested workarounds!