Your example code looks like C#, and in C# you have to use the typeof keyword to pass a type.
private GUITexture fire3 = fire3obj.GetComponent(typeof(GUITexture)) as GUITexture;
I've also added a cast at the end, which is also required under C#. If the variable fire3 is null after this line of code, GetComponent was not able to find that component type on that object.