express.exe is the main executable for MP3.com PLuS Express player.
It is a media manager allowing you to create play lists, burn custom CDs and transfer songs portable MP3 players. This is a non-essential process.
Disabling or enabling it is down to user preference.
Non-system processes like express.exe originate from software you installed on your system. Since most applications store data in your system's registry, it is likely that your registry has suffered fragmentation and accumulated invalid entries which can affect your PC's performance. It is recommended that you check your registry to identify slowdown issues