CCP has completed its downtime migration of the DUST 514 beta onto EVE's live Tranquility server. The company has published an extensive FAQ entry that aims to answer everyone's questions, including how capsuleers can rain fiery hot death down on their terrestrial mercenary counterparts.
As it turns out, ground forces can't fire back just yet, but it's also not possible for EVE pilots to hop from planet to planet sowing wanton destruction in their wake. Orbital strikes must be requested by DUST 514 players. After the request is made, any EVE pilot allied with the relevant militia and possessing the appropriate tactical ammo may answer the call.
There's much more to it than that, of course, and the EVE wiki has all the specifics.