Convert to MP3 BEFORE Upgrading to iTunes 7.2!
http://www.eff.org/deeplinks/archives/005285.php
apple has stated that this is a bug in iTunes 7.2.0. and will be fixed in a future release
Then the smart move is to not upgrade and wait till a fixed version is release.
Absolutely, 7.2 has no real feature other than DRM free tracks which are not even on iTunes yet so stay with 7.1.x until its fixed