Dashley,
You can make a freeze frame of the image you want, put it on the layer above your main video and crop it in the motion tab. If you want to go the Photoshop route, export the frame as a still image, take it into Photoshop. Duplicate the layer, (I always do this so I have the original image), turn off the base layer, with the duplicated layer as the active layer, cut out the portion you don’t want. You should see the checkerboard background where you have deleted portions of the image. Now use the wand tool to select the checkerboard, then select inverse from the Select menu, then click the channels tab and click on the “save selection as channel” button at the bottom of the channels window and you should see a new channel added called the alpha channel. Save your image as a Targa file 32bit (second window that pops up after clicking save). Import this file into FCP and lay it on top of your primary video layer.
Jamie
Dual 2.5 G5
FCP 5.1
Kona 2
XRaid