If the bike's frame size is in the neighborhood of 54 cm, your easiest conversion option is to bring the bike by my place. I dig the Volpe. I'll trade you for something else with a flat bar. ;-)

Seriously, though, you've got a few different things to think about:

• First, and most obvious, the handlebar.
• Depending on how the frame fits your wife, you may want a shorter/higher stem. You could potentially need to replace the stem anyway if your new flat bar doesn't have the same center diameter as the original bar and stem.
• You'll need to replace the brake levers and shifters. Your new brake levers will need to match your brake type (cantilever?). You'll need to make sure you're not using levers for the wrong type of brake. Likewise, your new shifters need to be compatible with your derailleurs. Depending on how your Volpe's equipped, which varied by year, your shifter and derailleur options will vary. How many cogs do you have on the freewheel? What brand/model are your shifters and derailleurs?
• New grips, cables and housings, etc.

Recent ones have STI shifters. Older ones had bar end shifters. And SunTour drivetrains if you go far enough back, which could make hexron's conversion a little more involved.