FOR THE PLAYER:
You must change the player in the config file. This is set up for Foobar2000 but it works with iTunes and Winamp as well. See below for Foobar2000.
; For a list of valid Player= values, check: http://rainmeter.net/RainCMS/?q=NowPlaying_beta#playerlist
Player=foobar2000
; NOTE!
; If you're using foobar2000, you must download the foo_rainmeter.dll plugin for foobar2000
; from http://rainmeter.net/RainCMS/?q=NowPlaying_beta (under 'Supported players').
I know it works with foobar2000, iTunes and Winamp