Install the most recent driver for your 9400GT. That appears to be 341.44 (32-bit):
After that, download the CUDA 6 toolkit desktop installer for win7 32-bit:
Run the installer, but deselect the option to install the driver that comes bundled with that installer. This means you will retain your 341.44.
If the toolkit installer complains about not finding a supported device, ignore that.
After that, things should work. Be sure to compile any codes with -arch=sm_10 switch (or similar) for your cc1.0 device.
If the above method does not work (i.e. a CUDA 6 compiled application or sample code gives you the error message that “driver version is insufficient for CUDA runtime version”) then I would say either you are not using CUDA 6 or else there is some problem I can’t help you with.
You’re welcome to try earlier versions of course.