If someone gives you the money without charge or consideration - that is considered a gift.
Gift is an income, but not taxable income. Please see IRS publication 525 page 33 for reference - http://www.irs.gov/pub/irs-pdf/p525.pdf
So - the recipient does not need to claim it on his/her tax return and does not owe any taxes. There is no limit on the gift value.
The donor - may need to file a gift tax return if the gift amount is above $13,000 per person per year (for 2009) , but there would not be any gift tax unless the lifetime limit of $1,000,000 is reached.
Refer to Form 709, 709 Instructions and Publication 950.
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