If you don't want to use your default music player when playing files from Tag&Rename, you can change the default to a different player by clicking the button with the gray folder and browsing for the new player in the pop-up window. When you have located the player, double-click it and then click Open. The Winamp field is used to play mp3s from the Winamp control toolbar.
You will then see the directory path of your new player in the field next to the appropriate player. If you want to resume using your default player, simply clear the player field data.