Sorting/Compilation question

Question

I've looked through previous posts on this topic and don't see one addressed to this specific question: Why does iTunes (I've got 7.0.2) assign music to the Compliations folder that really isn't a compilation?
I've been trying to build separate libraries of music -- one of aac files, for the iPod, and one of aiff files, for playing music through the computer -- and iTunes seems to make this a difficult task. Case in point: Pink Floyd's Ummagumma, a 2-disc release -- iTunes assigns disc 1 to iTunes Music > Pink Floyd > Ummagumma, but sticks disc 2 into iTunes Music > Compilations > Ummagumma.
It's a rip of a CD I own, and imported as aiff and then converted to aac. I used the latter to load on to the iPod, but kept the larger files because I can hear the difference between compressed and non-compressed music in my home stereo. But come to look at how these are filed, I've got nearly three dozen albums under "Compilations," two-thirds of which are by a single artist or group. I can understand albums that would feature multiple artists, but why does iTunes separate out the others?
Tom
PowerMac G5 dual 2.5GHz, 1.5GB; iBook G4 1.33GHz, 1GB   Mac OS X (10.4.8)   200GB&500GB LaCie FW HD, 16x LaCie LightScribe

Answer 1

Zang! Exactly the solution for which I was searching. Thanks.
Tom
PowerMac G5 dual 2.5GHz, 1.5GB; iBook G4 1.33GHz, 1GB   Mac OS X (10.4.8)   200GB&500GB LaCie FW HD, 16x LaCie LightScribe