I want to use emacs in terminal mode, but in Ubuntu 11.10 the bash terminal already has many Alt started shortcuts, how can I handle with that ?
You might want to consider using a proper terminal emulator instead of the gargantuan kraken-sized beast Gnome ships with. I suggest urxvt, or sakura if gtk is a must.
That being said, Emacs technically doesn't use the Alt key. It uses the "meta" key, which happens to be mapped to the alt key on modern systems, but that isn't mandatory. For one, you can use any
Alternatively, map the meta key to something else. This is explained here.