Ant Missions:

When the game loads up, hold shift & left-click on the speaker 
located at the top right hand corner. 

Queen Ant:

On the last Ant mission save your game and then load up a build-
a-base mission. Sell some buildings and you will hear "New 
Construction Options". It is now the Queen Ant becomes available.

Tesla Tanks in Skirmish:

When you enter Red Alert, click on the New Missions bar. Go to
 the mission The Legacy Of Tesla. Build up until you can produce
 Tesla Tanks. Then abort the mission. Click on Multiplayer Games
 and select Skirmish Mode. After you start a game Tesla Tanks
 should become available.