An Irish "Millennium" coin, with a face value of one Irish punt (or "pound"), is worth about US$7.50 in Uncirculated condition and about US$8.50 in Proof.
Please post a new question with more details. The U.S. is the main country to use Liberty on its coins. Britain is the main country that uses coins denominated in pounds. You'll need to provide more...
There are several million counterfeit British pound coins in circulation - sufficient that the UK Govt is thinking of recalling them and issuing new ones. The chance of your coin being genuine is not...