.zip to .jar?

[jits]

hi guys am having problems changin games from .zip to .jar because when i change it, it still ends with .jar.zip and when sent to my phone it still wont work how can i change the .zip to .jar correctly? and wot am i doing wrong im using windows xp
thank you guys

[ianb1985]

Open up any folder and goto tools/folder options/view then in advanced settings box under hidden files and folders uncheck "hide extensions for known file types"