So...how do you even start the game? I'm on the player select screen and I can't select anyone. I can only move the cursor around. Is there anyway to change the controls so that you can use a controller?
There's a cursor by the player's names, for P1 it's a red circle. Move your cursor over that and hit it. Then scroll to whatever character you want.
As for gamepad support, download Joy2key or Xpadder and you can set them to whatever buttons you want.
Here's a picture for clarification.