How to stop redirect on incorrect username/password

Hi! I have a problem I can’t solve by myself…and I nedd some help PLEASEEE :)!
I’m going to pubblish a blog that now it’s running on my private PC. I’m using a special slide in javascript where i put login/register/lost pwd forms.
Everything seems to be ok but that redirect on incorrect (or empty) username/password. Everytime it happens wp redirects me to the standard form with the shake javascript effect.
I just would like to redirect users to home_url() and show some message there (also using msgbox). I had a look to the code but I still don’t understand how can I do it.
I don’t want to use plugins!
Help me pleaseeeeeee! Thank u!