Hi evil_pro,
If all your songs contain the correct info in their tags (metadata) that you want to sort by, then there is already a way to sort a playlist editor listing by the desired tag.
The info displayed for each item in the playlist editor is collectively referred to as it's title. You can use the ATF (Advanced Title Formatting) option on the "Titles" tab in Preferences, to make a custom title string that places the tag you want to sort by 1st in a title string (e.g. %album% %track% %artist% - %title%). You can use the keyboard shortcut Ctrl+P to open or close the Preferences window.
You are given the option of re-displaying the items listed in the playlist editor after making a custom title string and closing Preferences (or selecting another Preferences option). You can change the ATF string anytime you want, but I would stop playback to ensure Winamp/WACUP doesn't get confused.
Then you can use the sort command in the context menu for the Misc button (at the bottom of the playlist editor), to sort the listing by the revised title info. Right-click on the right-most button in the group of 4, point to "Sort", and click on the "Sort list by title" command. You can also use the keyboard shortcut Ctrl+Shift+1, when the playlist editor is the active window/panel.