Need to Get Password from Computer on same network

Here's the deal. I want to learn how to get the password from a computer on the same network as me. Its my house network, there isnt any fancy firewall crap setup or anyone. I just need to know what programs are out there and what steps i need to take to get the password from another computer across the hall thats on the same network as me.

Thankyou.
We are both using a router, and running windows xp home.

 

No hacking tips on Afterdawn. Bye.