The only way to find out is to look at the case notes. Different DVDs come either as a stand alone version, or will have other versions as well. Personally, I find it annoying when I buy a Blue-ray version and see that there is a 'normal' version as well!
It is stated in the bluray case if it is 3D. go to bluray.com to get a list of 3D titles and find what you are looking for. And by the way hope you have the 3D glasses.
On another note, some 3D HDTV is capable of converting 2D (normal copy) to 3D but still the 3D copy is way much better.