Try copying the DLL's to a custom folder in your project. Then in the installation project add that folder to where ever the executable is located. That won't register the DLL to the system but it's a quick work around.
You could also just change the target platform to all machines. Usually by default that will install the 32bit version first. However , you would just need to change it back every time you compiled your project for testing.
Double check your configuration manager to make sure you are targeting x86 computers only. The project shouldn't even run without that setting on x86 but you never know.
Also just double check to make sure they have the correct version of Direct X 9.0c installed on the target machine.
Last but not least. Assuming you have VS 2010. Just upgrade to Visual Studio 2010 then deploy it. I've never heard of issues with 32/64 bit deployment on VS 2010. VS 2008 was built when 64 bit machines where still not very popular and unsupported for the most part and I know it has some issues with deployment to 64 bit machines.
" The best slaves are the ones who think they are free. "