1.The older PowerPoint files came with a .ppt extension. You will need to open it in a newer version of PowerPoint and send save it with a .pptx extension. This is normally a PowerPoint 2003 issue which 2010 should have been able to fix.
2.Now that you have created a new file you need to make a copy of the file;
3.Now you need to rename the file from .pptx to .zip (myfile.pptx rename ot myfile.zip);
4.Now extract the files from the zip file;
5.Got in the extracted files directory and into the media folder (ppt > media folder)
6.You now have all the audio files for the PowerPoint file;
7.Convert the .wav file to .mp3 with Audacity which is free.
8.Now edit your PowerPoint file and replace the abc.wav with abc.mp3