A question for tax return file

I have a question about how to file a tax return. My son is 19 year old and is in college(freshman) now. He earned $ 500 in 2006 summer job and has $1250 scholarship in 2006.So his total income is $1750 in 2006.

1).Does he have to file tax seperately?
2).Can we ignore his earned money but still use him as a dependent?
3).Should we include his income in our gross income and to file tax return?

Thanks in advance!