How can I activate the "change user" option in my start menu? I mean the option that lets you login with another user name without closing the actual session.

TweakNT doesn't work with my OS.

Do you mean Fast User Switching?

If it's fast user switching you mean, then you just go to "Log Off", and it should give you the option to "Switch User"

Yes, you're right. I said "change use option" because I was translating literally from Spanish.

Do you know how to activate this option?

HandyBuddy, it doesn't appear in my Windows Server 2003 Enterprise Edition