mp3 repeat and recordiong freerware help!

i want to convert a .ppt/pps slideshow, that is 7-20 minutes long into an .avi

I found freeware to do it, EM Free Powerpoint Video Converter.

it worked great on the visual, but did not capture the soundtrack of the .ppt.

i have the .mp3 song, but it is only 3.5 minutes long, so the converter truncates the slides when i use the shorter .mp3

what freeware is out there that I can use to create a "looped' recording of the 3.5m .mp3

into 7 or 10 minutes long?