CB - Editing Problems

Throughout using the programme 'Premiere Elements 8.0' we have encountered some editing promblems. A previous shot we had planned which would allow us to edit different clips of other footage onto the screen. The shot was of the protagonist looking at different moniters acting as cctv footage linking to the lyrics of "I'm watching you". However the programme is responding very slowly and therefore we have to render the footage after every slight change of editing. Furthermore the more clips we put on it the slower it gets and more problems we come across. For example, after putting certain different clips on the screen it deletes other sections of the footage.