My host file contains ALOT of other sites that I've had blocked (53,680 of them to be precise)
Instead I will explain how to do it because it's quite simple
1) go into
C:\windows\system32\drivers\ect
2) open the file "HOSTS" with notepad
3) goto the bottom of the page and paste what you want blocked
127.0.0.1 armedass.ms12.gamespy.com
127.0.0.1 armedass.master.gamespy.com
127.0.0.1 armedass.available.gamespy.com
4) save it
I'm gonna make a new modified HOSTS file anyway and see if I can get it hosted here