I am hoping you got your answers, if not I have some.

You need to have your niece ss number or ITIN number to be your dependent for 2008 tax filing. 

You did not mention about her age, because she is under 19 or under 24 and full time student, living with you 6 month and over and support over 50%.

Lack of SS number or ITIN number, she cannot be your dependent for 2008 tax filing purpose. Therefore you have to file yours as single or whatever filing status you do. Once you get your niece either ss number or the ITIN number, then you have to amend your 2008 tax filing. On this amend you claim you niece as your dependent and you will get the difference.

Again, instead of bugling mind, I would have visited nearby Tax Preparer’s office and would have got right answer for peace of mind. As I said, you do not have to pay a dime. Everyone is in March Madness, they are napping lack of customers.