[H] Vista64 certifie driver

[Winterlight]

I have a USB to Serial Port adaptor that Vista 64 will not install. 
It sees the adaptor, it finds the driver, but says the driver isn't 
signed and informs me that it won't install anything driver that 
isn't signed. It doesn't give me the option of do it anyway. Is there 
any way around this?
 thanks