You can upsample from the DSP Studio in Media Center. To get to the DSP Studio, go to: Tools -> Options. In the options window, select the Audio tab on the left, then, on the right, click "DSP & output format", which is right below Settings. This opens the DSP Studio window. Make sure Output Format is checked on the far left, and from the box in the lower middle you can select source sample rates and what to upsample them to.
