The iPhoto library is located as follows:
Hard Drive - Users - "your account" - Pictures - iPhoto Library.
"your account" is the account you used when you were running OS X from this drive.
Hold down the Option Key and Drag the iPhoto Library from its present location on the OLD hard drive to the identical position on the NEW hard drive. By holding down the Option key, you ensure that you only drag a copy of the Library to its new home and, if the worst happens, you still have the original on the old Hard Drive.
Do not use the bar on the left hand side of the windows to get to the Library, instead navigate in the window itself.
Worked for me lots of times.