To convert a PowerPoint slide into an .eps or other high resolution file type that can be placed into InDesign or Quark:
1. Save the PowerPoint slides as a PDF
2. Open the PDF in Adobe Illustrator
3. Resave the file as an .eps or .ai file
You should be able to edit/modify the text and graphics that were created in PowerPoint. The text and graphics that were originally placed in PowerPoint as tiff or jpeg files will not have editable text.