Play as NOD in Skirmish mode of demo
     At  the  skirmish options menu, hold N and click you army to make
NOD as selectable option.

     To switch back, hold G and click your army to make GDI selectable
again.

This works with the computer army as well.


Play as the Scrin
     To  play  the  secret Scrin campaign, finish both the GDI and Nod
campaigns. This will unlock the Scrin campaign of four missions.


Increase Starting Credits in Skirmish Mode
     Go  to "C:\Documents and Settings\User\Application Data\Command &
Conquer 3 Tiberium Wars\Profiles\ProfileName"

Make a backup of "skrimish.ini"

Open the "skirmish.ini" file

Change the number "10000" to the desired amount of credits