There are such as thing as mixed mode CDs that contain both audio and data but it is not the norm. True that iso9660 is the default for run of the mill for
data CDs but not all. You will have to tell us exactly what you mean by run of the mill. Is it audio, purchased, something you burned? If it was something you burned then tell us how and using what OS? If you burned it using Vista then it could be a packet writing CD which is a UDF filesystem. And there are several versions of packet writing. Or is it really a DVD?
BTW what version of linux are you running?
http://en.wikipedia.org/wiki/Enhanced_CD