If you are in CS4 then create a new sequence in the correct preset for your footage and the 1080 frame size. copy the edit from the original timeline and paste into the new 1080 timeline. You may have to check the scale to frame is off and then make sure you select all your clips to remove effects ‘sacle’ to bring them to fit the timeline frame as they should.
If you are in CS3 then make a new project with the correct timeline frame size preset (1080) and then import the original project. I think from memory the timeline you import will now be the same as the projects timeline and the sizing issues as i mentioned above to make sure the 1080 media is fitting to the 1080 timeline frame properly.
– JB
Jon Barrie
aJBprods
http://www.jonbarrie.net