These are Windows 7 directions for adding a Printer which is connected to an Airport Express on your network.
First get your Printers IP address.
Make sure that the printer is connected to the Airport Express and turned on.
Start > Control Panel > Devices and Printers
Add a printer > Add a local printer > Create a new port:Standard TCP/IP Port > Next
Hostname or IP address = your printers IP address
In the Port name field, add “IP_” before the IP address (without the quotation marks)
Check the box “Query the printer and automatically select the driver to use” > Next
Windows will take a moment, then it will require Additional port information
Choose Custom > Next
Choose your printers driver. If it is not listed, try Windows Update or Have Disk > Next
Enter a Name for your printer > Next ***(I choose to include in the name, that this printer is on the AirportExpress, this helps differentiate between the printers when plugging in the printer via USB)
The printer will begin installing…
Check “Do not share this printer” > Next
If you want, you can check the box to set the printer as the default printer
Try printing a test page > Finish