mouse projection ???

Hi !
I'm a newbie in OpenGL and have a question.
I have a plane on (x,z)axis, and i'm in a perspective world.
I can rotate and translate the worls.
I want to find the coordinates of the plane's point corresponding to my mouse location.
Can anybody have an idea ?
Thanks

[ZbuffeR]

Use gluUnProject to get the 2d coordinates of your 3d vertex position, using the specified projection. http://pyopengl.sourceforge.net/documentation/manual/gluUnProject.3G.html