setup wifi home network with imac and pc

airplanesrule, Welcome to the discussion area!

Sorry but you probably can not use the AirPort Express (AX) to provide a network connection to your PC. The AX's Ethernet port is ONLY active when the AX uses WDS to wirelessly join a network.

Most 3rd party routers are NOT compatible with Apple's WDS.

The AX can easily join your wireless network as a client. But in this mode the Ethernet port is NOT active.

What is the brand and model number of your wireless base station which is creating the wireless network?

I bought an airport express last year to use on my strictly Windows non-wireless network. Worked great and I was able to stream my iTunes over my home stereo and create a wireless home network. (I plugged my ethernet cable into a router, and than used one of the router's ports to contact another ethernet cable to the aiport express.) Got a new iMac a few months back and it works with that old airport express too. I can't give you much technical help, just don't give up, because it works for me. I can even copy files from my Windows computers (XP and 2000) back and forth to my iMac.

Mac OS X's Internet Sharing is not compatible with WDS therefore you can not set up a WDS network with an AX. Therefore the Ethernet port on the AX will NOT be active.

but what is wds??

WDS is "Wireless Distribution System". KB 107454, Using the AirPort Admin Utility to create a WDS network with multiple base stations

do I need to use it to set up my wifi??

Normally no. You can configure the AX using the directions in KB 302153, AirPort Express: How to join an existing wireless network in client mode to have the AX join the wireless network. But the AX's Ethernet port will not be active.

You will need to get a wireless (USB, PCI, or Ethernet) adapter for the PC to give it the ability to connect to a wireless network.

Sorry but someone with Windows experience will need to drop in and give you some suggestions.