Userscripts.org

It's very simple really:

1) Adds a select dropdown component.
2) When user changes the value of the dropdown, script modifies the server number in the action field in the login form:

For example say you would be logged in to 124 by default.
If you change the value into 120:
< form action="www124.popmundo.com"> becomes < form action="www120.popmundo.com">

That's all what the code does. And you will login to the server number of your choice.