Fast batch encoder to change video FPS?

I need to convert 27 divx files from 15 FPS to 30 FPS.
Files are between 50 and 80Mb.
Why?
I converted an old Divx DVD player (sigma EM8500) and was able to put a HDD inside. Check www.sigmaplayer.com, russian site, but google translation helps, firmware 1.3 works well.

The only problem is that 15Fps files are played at 30FPS (or 25 probably), so you understand that everything is sped up quite a bit.

by changing the FPS back to 25 or 30, I'm sure everything will be back to normal.

Thanks a lot for any help.

Problem solved, this is not a double post since I close the discussion myself ;)

Plain Old VirtualDub was more than enough to complete the task.

Thanks