If you have version 6 (I can't remember if it was in 5.5) you could use 'Extract'. Use the pen on the Extract screen to outline the bits you want to keep, make sure that there are no gaps in the outline and then use 'Fill' on the bit you want to keep. Click the 'Preview' button and Photoshop will remove all the unwanted bits. Use the edge touch up tools if necessary before clicking OK. Hope that helps.