any one familar with makeing virtual cockpit using gmax? and also does any1 know how to use that cockpit u made to put it in an aircraft?               please explain

Whait, in about 3 minutes you'll have tutorials....

There are several ways to approach this.

#1 - If you want to "add" a VC to an existing compiled FS9 (or earlier) model, you're out of luck, and cannot (the VC models is incorporated into the mdl file.)

#2 - If you want a different VC for an FS-X model (one made with the FS-X tools and that has a SEPARATE interior model, technically you can.  It's no different from creating the external model (except you're modelling the interior, of course)  You still have to create animate and texture all the parts, incuding the gauges, VC panels, etc. compile the model.  Since you'd be relacing an existing VC, make sure you rename your new VC interior file with the corresponding name.