Pavr27,
whether your printer is connected via Ethernet or USB does not matter to AirPrint for Windows. The question is who 'owns' the printer, in other words where will the print queue be managed ? If you have a print server in a router for example, then the printer owner is the router. If the printer is attached to a computer, then that computer owns the printer.
The rule for AirPrint for Windows is that the printer has to be shared on the computer running AirPrint. If the printer is connected to that computer, fine. If the printer is connected to your router, but there is no print server in there, then each computer owns the printer because each computer spools the print jobs. The all you have to do is share that printer on the computer where AirPrint runs.