depending on your approach..your window can be just 2 sided plane, with different RGB (each of 20 windows), or, if you using 3DSMAX, you can do same thing, asign RGB values to your windows, and then assign 19 windows to 1 you choose as a parent..export as 3DS, and then load your windows in to Blitz3D, and apply EntityAlpha Window,0.5 and all of them will be with same transparency (trough 3DSMAX transparency you can export already on your mesh), or if you want to set up different transparency for different window, then load your window mesh with LoadAnimMesh and then acces each window entity trough FindChild command...its up to you anyway..