Windows 7 64 bit or 32 bit? Only 64 bit Windows refuses to install unsigned drivers, on a 32 bit system you can install unsigned drivers, it is only a warning windows displays.
As I am interested in this problem, I did search microsoft knowledge base for updating drivers via windows update.
First of all, windows only can find drivers for stuff directly connected to your pc. It is technically impossible automatically finding drivers for a shared printer on a linux host.
The other problem, windows update button is greyed out: the only idea I have is that microsoft update is generally deactivated on this machine.
The third problem: as windows "sees" no new unknown printer, there is no need to update drivers.
So, finally: the ways to install a printer driver are shown (thanks to the other users who followed my wish and used english here). If (what I still cannot believe) windows does not support oldschool laserjet dinosaurs, try to use a appropriate driver from windows, a Laserjet 4000 driver should work fine.
Alternativly download the HP universal printer driver. This one exists for 64 bit systems too and is digitally signed. This driver works fine with nearly every HP laser printer.