Other API's to complement OpenGL for games?

OK, here’s the deal. I am an aspiring game developer, working on a 2d game engine in my spare time. I have a data-driven 2d directx engine that has some pretty basic functionality…I have a (scaleable) character that can move from screen to screen. However, I want some of the more advanced graphics doodads that require a 3d api, such as transparency. Being able to map a texture onto a 3d surface and rotate it really makes special effects much easier. Anyways, here is my question. I want to replace the functionality of my 2d rpg game engine with opengl. Is this a good idea, and is it feasable? Is it possible to use opengl for all of the graphics in the game? i.e. no directdraw / direct3d at all? How would I handle sound, input, multiplayer, etc? Essentially, is it a good idea to do my graphics with opengl and use directsound and input for everything else? Any advice would be appreciated. Thanks.

SDL for basic application and input.
OpenAL or FMOD for sound.

it is very much possible. you should give it a go. you can still use direct input and directsound, but use OpenGL for graphics.