If you have not set up a Facebook Profile your ID will be easy to locate.  While on your Facebook page, click on the link to go to your Profile which is found next to your Facebook Home button. 

In the address bar you will find your ID, which should be a long string of numbers. 

Example:
http://www.facebook.com/?ref=tn_tnmn#!/profile.php?id=123456789012345

id=123456789012345 is what we need.

However, if you have set a Facebook profile you can still get your ID.  Make sure you are on your Profile page, as listed above.  Them mouse over your Profile picture.  On the bottom of your window in the "Status Bar" will be another 'address'.  Your ID will be a long string of numbers after the "a." and before the second period. 

Example:
https://www.facebook.com/media/set/?set=a.123456789012345.218781.644017919&type=1

a.123456789012345 is what we need.