If two different people use the same PC can they each set up their own Instant Messenger?

Don;t save the user name and password. Each person logs in with their own.

Sure, just have the other individual set up his/her own messenger with password and all. Then all they need to do is log off one and log onto the other. email same way.

yes, by setting up different user accounts

As already said, just log in under different IDs

yes. Each one sets up their own user name and password.

Yes but only one of you can be signed in at once

of course. If you have aim just create different sign in names

What do you mean? like different programs or different accounts?

yeah if they switch users there can be over 4!

yeah just have 2 diffrent accounts.