If it's xp, it would usually reside in the system32 folder. Do this: Start>right click My computer, select manage from the menu box, click device manager, locate the card on the device list, double click it, then select drivers, then driver details & all will be revealed.
I would be leery of digging round the windows folders though - you could cause more problems than you solve - the obvious thing to do as mentioned already is to download the driver & transfer it to your mates using a datastick, which are neither expensive nor hard to come by.