Why is my artist's not included together as one?

For example, I have almost every Dave Matthews Band album, however, Itunes decides to break all of his albums up into about 6 different artists. This is very frustrating as it makes no sense to me and is difficult to find particular songs. I primarily use Windows Media Player as a PC music player as it is simple and efficient. I only use Itunes to put music on my Ipod Touch. However, as stated, Itunes decides to split his albums up between multiple artists. (Dave Matthews, Dave Matthews Band, Dave Matthews Band; Maceo Parker, etc.). Windows Media Player properly understands and organizes all of his albums together under a single artist. However, Itunes splits him up into these various artist names and makes it very painstakingly difficult to play certain albums/songs due to the mix up of artists. Is there any easy way to fix this? or is Itunes just a lost cause and an unfriendly user interface? Any advice to fix this situation is greatly appreciated as this problem greatly irritates me. (FYI, several other artists in my collection experience the same problem, likewise, this problem only exists in Itunes and not WMP)