The keyword I am entering in the Gaussian interface Chem3D provides is being ignored.
The CS Gaussian client may not support the keyword you are using depending on the version of G98W you are using. To work around the problem, create a Gaussian Input file using the Chem3D Gaussian menu. Then open the Input file in your favorite text editor and add the keyword to the Input file. Save the Input file and then you can Run the Input file using Chem3D's Gaussian menu. The input file bypasses Chem3D and goes right to G98W, so Chem3D can't strip it out again.
The header of the input file might look something like this:
# RHF/STO-3G Pop=(Minimal) %mem Test
Where "%mem" is the added keyword in this case.