To convert tempo in Digital Performer,

• First highlight the soundbite(s) and go up to the Audio Menu
• Select Time Stamps and Set User Time Stamp from Sequence (this will time stamp your soundbite)
• Go to the Soundbites Window
• From the Mini-Menu, select Automatic Conversions
• For the "Convert to Sequence Tempo," select Whenever File Tempo Doesn't Match The Sequence Tempo
• Close the Automatic Conversions Window
• In the Contro Panel, change your Sequence Tempo

You will see a Background Processing window indicating that Digital Performer is converting your soundbite to match the tempo change.