....is it possible to connect a VU meter to a computer to adjust the volume on itunes?
I can't help with information concerning the physical connection but I can make a suggestion concerning metering in general. If you are talking about an actual VU Meter (with the needle) you would be better off to look for a PPM (Peak Program Meter) of some type.
The problem with a VU Meter is that it is ballistically very slow compared to a PPM. This means that the needle is too slow to reflect the actual level that is going through your equipment. By time the needle travels upward the peak has come and gone and the needle falls. The result is that you end up with distortion from peak program levels that occurred but which your meter was too slow to detect.
A PPM, on the other hand, reads peaks instantly.
ryck