Evaluation of MO's from ab-initio calculations

I'm looking for some code that I can use to compute orbital and density values on a grid from ab-initio (Gaussian/Gamess) calculations. I'm aware of the MOLDEN code but this is not suitable for my purpose. What I'm really after is a Gaussian CUBEGEN like program that I can use like a library.
Alternatively if someone can point me to some literature I can probably cook something up.
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