I take it that you want to delete all your music in iTunes and on your iPod Touch in Windows.
For your music in iTunes, what you is click on the Library/Music and then select Edit/Select All. This will select all the music on your harddisk library. Then just do a Right-Mouse Click and select Delete.
For your iPod Touch, select Devices/Music and repeat the steps above.
By doing that, it would remove the music from the iTunes library and that of the iPod Touch. It does not officially delete the music on your computer and you can reorganize the music on your computer and iPod as you want.