i can load and render a 32bit , uncompressed tga file in OpenGL. i want to create a fade in and out effect by controling the transpareny level. i am working on a 2d project, so just sprite transparency effect is needed. how would i do this?

Short answer: the keys are to enable blending, set the appropriate blend mode, and render your graphics in the proper order. You can find more info in the Red Book or at the Nehe site (or through google).

[Edit: If it's just sprite transparency you're interested in, you might look into alpha functions instead.]