Easy enough:
Assuming Win7:
Control Panel -> Device Manager
Find the device in question (if Windows knows what it is, and has a driver installed for it - under 'Network Adapters', if Windows DOESN'T know what it is, under 'Other Devices' with a question mark and a generic 'PCIe device').
Right click the device, go to 'Properties', then click the 'Details' tab. In the drop down box, select 'Hardware IDs', this will give you the hardware/vendor IDs. Then google it. (Right click the ID, select 'copy' then paste into the browser search of your choice).