Horribly unlikely to see the use of Nuclear weapons in space.
Nuclear explosions or any kind of explosion in space is completly useless compared to their use in atmosphere. The reason why explosives are so effective is that they create shockwaves trough the air, exponentially increasing their destructive power.
In space there is nothing to create a shockwave. The explosive energy in space would simply flow in the direction that offers the least resistance. In other words, towards the vacuum. Plus, nukes are big and they are difficult to deliver in space, where you have an easier time intercepting them.
The most likely weapon you would see used in space warfare are Kinetic Impactors. Plain old simple bullets. Most likely cannons and machine guns, firing low caliber, high velocity rounds.
http://en.wikipedia.org/wiki/Almaz#Defense_measures
The Russians tested the use of cannons in space already.
But you are unlikely to see Battleship sized cannons on ships, because in space firing them would be a nightmare. They would act as propulsion, so you couldn't really fly straight or aim while firing. Plus the vibrations they would send trough the gun and the ship could break the ship or gun apart.
Again if you want to kill people on the ground from space, you would still use the same thing.
You don't need to fire big complicated nukes. Just aim a high density metal penetrator at something, fire it at an angle that prevents it from burning up during descent and enjoy the show. Descending from space at stupid speeds they could wreck anything, causing huge booms. But again you cant make the round too big, otherwise atmospheric friction would burn it up before it can hit anything.
Space warfare would be very different then in movies.
The whole deal is a mathematical game of orbits, velocity and angles. You don't need very big guns, you all you really need is to hit things with a solid slug.