It seems to follow from a certain kind of realism about metaphysical possibilities that a version of the cosmological argument goes through. The idea is that if the space of possibilities exists, then it exists necessarily. The actualized concrete events of the world are contingent and depend on the necessary space of possibilities.
There are many variations, but the cosmological argument states that the chain of events needs a necessary first cause to get started. Or else it is cast in terms of arguing that contingent things ultimately must depend on a necessary self-existent thing. In the model under consideration here contingent things (events) are actualizations of possibilities. A given event is subject to causal constraint by prior or adjacent events but is always also dependent on the space of possibilities.
There seems to be no well motivated reason to consider an objection involving, say, an infinite chain of meta-modal spaces upon which the first-order space of possibilities depends. So, the space of possibilities would be a self-existent necessary entity and the argument goes through.
[UPDATE: 5 February 2009 -- This modal realism-inspired cosmological argument should not be confused with other arguments which goes by the name "modal". These arguments (which doesn't work IMO) try to use modal logic to imply theism: see discussion here for instance.]