Halo has lots of vehicles:

As originally announced, Halo was also going to feature combat on and underwater, however there are apparently no such vehicles in Halo at this point.

Vehicles may be driven either by the player or AI-controlled allies in single player. Vehicles may also be stolen from opposing forces. Vehicles can even apparently be driven into certain interior structures on the Halo, as seen in some of the more recent gameplay movies.

Early on it was speculated that perhaps dropship piloting would be a possible role for Halo players, especially in network play.

However, currently players cannot control the dropship, and in the Xbox release version of Halo there is no Internet multiplayer.