Hmmm...While goldie is absolutely right about how irresistible grace and limited atonement are necessary as part of the Calvinist system of soteriology, he's not entirely accurate with regard to Calvinists being "uninterested" in preaching the Gospel.
The fact is, some of the greatest preachers in history have been Calvinists. Some of the greatest Evangelists as well. C.H. Spurgeon was a Calvinist, as was Jonathan Edwards. And don't forget George Whitefield! Whitefield was a "Calvinist Methodist" who essentially became the catalyst for the first Great Awakening in the American Colonies. Yet, he and John Wesley were lifelong friends who prayed for and supported each other.
Certainly there ARE hyper-Calvinists that believe preaching the Gospel is unnecessary as God knows His elect and will save them irresistibly. The Primitive Baptist Churches in my home state of North Carolina are examples of this belief -- and so are their empty, shut down, old church buildings. Other Calvinists, however, have allowed their soteriology to run smack dab into reality -- if they don't go out LOOKING for the elect, then the "elect" will find their way to Arminian churches!
JDale