CUDA dll(64bit) vs Microsoft Excel (32bit)?

Hi all,

I am working in a bank and we use Excel to prepare data before triggering our own pricing dlls, which we hope to accelerate using CUDA GPU.
Our setup is: Win7 64bit / Windows Server 2008 R2 x64, with Excel 2007 32bit. For now the CUDA installed is 64bit.

Regarding 32bit vs 64bit, can ask which way is possible? (or prefered?)
method 1: develop 32bit CUDA dlls (using current 64bit CUDA installation, whether possible?), then use seamlessly with our existing Excel & other Dlls
method 2: develop 64bit CUDA dlls (using current 64bit CUDA installation), then reinstall Excel to 64bit (Excel 2010 64bit), and rebuild all our other Dlls to be 64bit
method 3: install 32bit CUDA (whether possible in our Win7 64bit?), then develop everything in 32bit.

Thanks.