FFmpeg is an open source media "swiss army knife". It can handle exactly what you're looking for, but it does require using the command prompt.
First download FFmpeg, any recent release will do. You'll need a program to extract the 7z archive. I recommend WinRAR (free trial). Extract ffmpeg to a folder, I used c:\ffmpeg.
Next open the command prompt (start > run > cmd.exe). And do the following (again, assuming ffmpeg was extracted to c:\ffmpeg.
c:\Users\media> cd c:\ffmpeg\bin
c:\ffmpeg\bin> for /r c:\Users\media\Music %i in (*.mp3) do ffmpeg -i "%i" -ss 0 -t 20 -aq 0 -y -acodec libvorbis "%i_clip.ogg"
Change "c:\Users\media\Music" to the folder that contains mp3's you want to create clips for. Refer to the ffmpeg manual for instructions on the various options (-aq = quality, -ss = skip seconds into file, -t = time in seconds)