Please specify - if your father and/or the mother are US persons? or they do not have any connection with the US?
Based on that you will determine if there are any tax obligations on your mother.
For your - as you received a gift - that is not taxable income.
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.
Let me know if you need any help.
As you mother and your father are US persons - there would be additional tax liability on their side.
Your mother should determine the basis of the property - that is mainly a purchase price.
Because half of the property was inherited by your mother in 2004 after your father died - her basis on that half is a fair market value of the property at that time.
Then - she will report the sale transaction on the schedule D part II - as long term capital gain.
Her capital gain would be $180,000 (selling price) - (basis) - and it is generally taxable up to 15% depending on her other taxable income.
As the donor - she 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.
as she transfered the money into the US - if the amount is more than $100,000, the person is required to file form 3120 - http://www.irs.gov/pub/irs-pdf/f3520.pdf (see instructions for details - http://www.irs.gov/pub/irs-pdf/i3520.pdf) to declare transfer from the foreign country. There is no tax associated with this form.
In additional - your bank might be required to report your transaction - so I would suggest to consult with the banker if they need any supporting documents so your transaction would not look suspicious.