Google is a US company and therefore subject to US laws which restrict
money flows to specific countries.
At the moment Cuba, Iran, Libya, North Korea, Sudan and Syria are on
that list, but it might change pending US foreign policy, and you
won't be able to signup until 2010 anyway, so check back then on the
situation.
The best way to do that is to subscribe to
google-summer-of-code-announce, and then read the Terms-Of-Service
when the program officially opens in 2010.