There are 207 cardinals. Of these, 117 were under the age of 80 at the time of Pope Benedict XVI's abdication and therefore are eligible to vote for the next Pope. Of the 117 eligible electors, two cardinals will not attend the conclave. One is an Indonesian who is in very poor health and the other, a Scot, who recently became the subject of a homosexual scandal.
Technically, any baptized Catholic male is eligible to be elected pope though in all practicality the next pope will be a member of the College of Cardinals. He could be above 80 years of age though the cardinals are likely to vote for a person is not likely to die or abdicate within the next year or so.
Here is a country by country breakdown of the 115 voting cardinals.
Here is the breakdown by continent/cultural region
Cardinals are not chosen proportionally. They are meant to be chosen on their administrative and theological merits. Both Pope John Paul II and Benedict XVI have done a good job diversifying the country's of origin for cardinals by expanding the Vatican's outlook past Europe. In fact, in 1903 over 56% of all cardinals were Italian and now that number has been halved. However there is still strong geographical bias.
The breakdown of the world's Catholic population is
If the breakdown of voting cardinals matched the breakdown of the world's Catholic population then the college would look like
Instead of worrying the dreaded "Italian bloc" which controlled the papacy for over 200 years before John Paul II, Vatican watches would wander what the Latino alliance led by Mexico and Brazil would decide.
Continuing on the demographic realignment theme, here are the countries with the most Catholics in order and their ranking with voting cardinals.
The country with the most Catholics without a voting age cardinal is Uganda with over 11 million Catholics, making it the 14th most Catholic country in the world. The country with the most Catholics without any cardinal is Guatemala with 8 million Catholics, making it the 25th most Catholic country in the world.
For the best update on conclave news I recommend New Advent which has a daily updated buzz indicator for all 115 voting cardinals.