I try to connect my electric guitar on leopard 10.5.7 but it doesnt recognize the line in!!!!!!!

It seems to be working for me here. I recon you got garageband? If so try pluging it into your all the sound ports you got. And also under system preferences, sound, Input select the plug you are using. When you dubble click your speaker in garageband make sure you configure the input source and set the monitor to on or on with feedbacksecurity (feedbacksecurity helps if the sound gets distorted to much).

Sorry for the wrong use of words my OSX is dutch so i have to translate everything XD.