These are loans to the IMF
http://uk.reuters.com.../idUKLJ48416520090320
It's like you saving money with the bank and them lending your money to get a failing business back on its feet
If a western national Government were to default, any western national government it would shake the confidence of the markets to the extent that it would make it much more expensive for all governments to raise money.
If Greece defaulted the markets would say "Nobody helped them maybe if we lend you money and you get into difficulty the same would happen"
it's in everybody's interest that confidence in National Governments is maintained