If you mean gravitational equipotential lines, they can't cross. The reason is actually kind of confusing, involving higher math than you are expected to know.
Note to chubby: Space-time is warped by gravity, in many physicists' eyes; it is actually the direction of the warping's being the same everywhere that provides the above result. Equipotential lines conceivably could cross, if the characteristics of the field were different, but the crossing lines would have to have identical potentials to each other, by definition -- I think this last part is what you meant. And no, no, you don't have to know any of this.
On the other hand, electrical equipotential lines can cross each other. For proof, consider the simplest such case that I can think of: an electrostatic quadrupole. Locate point charges of +1 at 2-d coordinates (1,1) and (-1,-1), and charges of -1 at (1,-1) and (-1,1). Now the x- and y-axes are each equipotential lines (with potential = 0), and they cross at the origin.
The reason for the difference is, as I said, mathematically complex, and you don't need to know it, but I thought I'd address the orginal question lest anyone become confused upon arriving at electrostatics.
Shrike