You need an older driver with cuda 3.2- something beginning about 263.xx
Cuda 3.0 would be something like beginning 197.xx
The trouble could be that the GTX560 came out after those - May 2011.
I am checking that but the info is a little hard to find...

Edit: it appears driver 275.27 might have been the first to support the GTX560
275.27 is still available http://www.nvidia.com/object/win7-winvi ... river.html
However Cuda 4.0 would be beginning about 270.xx.
It could be that you are out of luck with the GTX560 for trying the demo.

The good news is that Refractive should be updating their demo version fairly soon probably based on beta 2.57 which will also allow people to try the 3d Max plugin as well.
Your GTX560 will definitely run that.
If you are keen to try Octane perhaps just wait off a little for that to arrive.
Feel free to ask any questions you may have in the meantime.
HTH