Originally Posted by the DOSBOX readme

Q: I can't type \ or : in DOSBox.
A: This can happen in various cases, like your host keyboard layout does not have a matching DOS layout representation (or it was not correctly detected), or the key mapping is wrong.
Some possible fixes:

1. Use / instead, or ALT-58 for : and ALT-92 for \.
2. Change the DOS keyboard layout (see Section 7: Keyboard Layout).
3. Add the commands you want to execute to the [autoexec]-section of the DOSBox configuration file.
4. Open the DOSBox configuration file and change the usescancodes entry.
5. Switch the keyboard layout of your operating system.

Note that if the host layout can not be identified, or keyboardlayout is set to none in the DOSBox configuration file, the standard US layout is used. In this configuration try the keys around "enter" for the key \ (backslash), and for the key : (colon) use shift and the keys between "enter" and "l".

Originally Posted by _r.u.s.s.

why don't you switch your italian keyboard layout to english one? on the bottom panell

the quick key for this is alt+shift