Take two equally sized sets of vertices, normals, and possibly texture coordinates (these can remain constant if you want). Then do something like this (this is linear interpolation, there are better looking methods):

  for(int a=0; a<VertCount; a++) {  Inter[a] = Alpha[a] + ((Beta - Alpha) * Distance);}  

Of course, you can unroll that, and you need to do it for all the data sets you''re working on (the vertices, normals, et cetera). Then you just render the ''Inter'' data sets. Another easy method for interpolation is cubic interpolation. There''s another called something like Catsmul-Rom Spline interpolation, but it isn''t as easy.

[Resist Windows XP''s Invasive Production Activation Technology!]