First burn the songs to a CD (this removes the copy protection of the original AAC file).
Then pop the CD in your computer, and open iTunes. From the iTunes preferences, choose 'Advanced', then 'Importing'. Make sure the importing prefs. are set to 'MP3 encoder' & the bitrate you want. Highlight the CD, then click 'Import' in the top right hand corner of the iTunes window. Once the songs are imported, highlight them, and choose "Show song file" from the file menu to locate them on your hard disk.
Drag them over to the other device, and delete them from your hard drive if you wish. You're done.