How to share an Internet connection?

Hey guys, my friends coming over tomorrow, and hes bringing his desktop computer.
Were going to be playing games up in my room. My computer is running off a wireless connection, the router is 2 floors down so a ethernet connection to it is out of the question. My desktop does have a ethernet port, so i could plug a crossover cable into it if you could share like that. My friends computer lacks a wireless card, and only has ethernet connections. I want to give him internet, by sharing my computers internet.

I have access to a crossover cable and ethernet cables if thats how you can share.

Thanks