Go to Window menu and select Links. When you select an imported graphic in AI, that graphic will highlight in the Links window.
To find the the folder where the graphic is, click the little triangle at the top of the Links window and select Link Information.
Remember that, if you're sending the AI document to someone, linked images must be included in the folder, just like fonts, that yu send to the other person. If you want you can select Embed Image from the nenu shown when you click that triangle. It's then part of the AI file and you don't have to send the separate image to the other party.
Using OSX 10.3.8 on a G4