I set up a shared folder in Parallels (use Edit mode on the virtual machine), and pointed it to /Volumes. Now all mounted devices are available in Windows via the Parallels Shared Folders shortcut.
[robg adds: This is a good alternative to creating shares for specific folders, as it gives you access to everything.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20061230224705532