I know that meybe this thread is not OpenGL, but I don't know where to put it... Can you use .tga as resource files? Or any other graphic extension besides bitmap... I want to make OpenGL screensaver for one game but I know only how to use bitmaps as resource...

Assuming your talking about Windows, any file type can be added as a resource. However, for non standard resource types you'll need to use LoadResource() and LockResource() to get a void pointer to the beginning of the resource as a file. Hopefully your Targa loader can work off of files in memory.