Running F@H as a text-only service is slightly faster (according to the FAQs). When minimize I have not seen near the difference that prophetic is mentioning. I do have a fast video card and that offloads the work from the CPU when I leave it as a screen saver, which is almost never.
2) To do that I should uninstall what I now have and then do a new install?
Wait until a work units finished so that you don't waste processing work units. Uninstall, then reinstall according to directions. It is faster to run the console than to run the full program, but again, not much.