so you should be able to enable the connection sharing and use the ethernet port to connect the pc's. your connection to the second pc would go this way. router --> into wifi card on pc 1 --> out ethernet port on pc 1 --> into pc 2 by way of ethernet.
i don't know what version of windows you are using but MS has some nice guides in the knowledge base on how to do this. as i said i did this a long time ago to share internet with an xbox 360 back when the wireless adapter was like $80 or so. it took me a while to get all the ports forwarded and such to the xbox but i got it working and it worked nicely once configured.
what windows version are you using, then google that version and "internet connection sharing"