This is a program of research activities broadly directed toward using the new ten-meter South Pole Telescope (SPT) to probe the nature of dark energy and inflation. The telescope and the initial detector array were constructed under a prior award, and science observations are starting during the austral winter 2007. This study includes support for operation of the SPT, storage and reduction of ... the data, and science analysis. The initial project is a few thousand square degree survey, using the Sunyaev-Zel'dovich Effect (SZE) to detect all galaxy clusters more massive than a specific limiting value, independent of their redshift. Combining these results with optical redshifts, both currently available and yet to be observed, will place tight constraints on the equation of state of the dark energy. SPT observations will also measure fine-scale temperature anisotropies, which can determine whether a departure from exact scale invariance exists, as is predicted by the current 'standard' inflationary cosmology. Longer-term projects include developing a new one-thousand-pixel, dual-polarization, multi-band polarimeter for the SPT, to measure the Cosmic Microwave Background (CMB) polarization anisotropy over scales of an arc-minute to several degrees. Measuring the angular power spectrum of the so-called B-mode polarization, as well as the large angular scale modes imprinted on the CMB by inflationary gravitational waves generated in the first instants of the Universe, exploits the unique and powerful capabilities of the SPT for research at the cutting edge of cosmology and astrophysics. The critical questions, and recommendations for research programs to help answer them, have been the focus of several national reports, including the 2000 NRC Decadal Report on Astronomy and Astrophysics, the NRC report Connecting Quarks with the Cosmos, the OSTP inter-agency report Physics of the Universe, and the reports of the Task Force on CMB Research and the Dark Energy Task Force. The science of the SPT research projects is at the heart of cosmology, is directed at answering some of these most compelling questions, and will have significant broader impacts throughout cosmology and physics. More broadly, the project contributes to the training of the next generation of scientists by integrating graduate and undergraduate education with technology and instrumentation development, astronomical observations, and scientific analysis. The SPT surveys will also lead to large, publicly available datasets. The sharing of forefront research with non-scientists extends beyond the university to both established and new programs based on exploiting the growing popularity of video and audio content on the web. The International Polar Year celebration also offers a special opportunity to contribute to public awareness of polar science.