I also have the same problem. I have Ricoh camera. It has worked perfectly with previous OS and iPhoto on my iMac. Now I have OS 10.5.6 and iPhoto 09 and the "problem writing to volume" message appears when I go to import photos from the camera.
I have repaired permissions and a whole range of housekeeping tasks. I have 173Gb of free disk space. The same problem appears with my Macbook running the same versions of OS and software.
The Ricoh Caplio Mounter driver (for OS X) allows me to see the camera files in Finder, where I can copy them to a folder on my desktop. I can them drag the desktop files into iPhoto and they appear there without problem.
I did have some movie (AVI) files on the camera but this type has imported previously without problems. They also import from the desktop.
I suspect there is an incompatibility between the Ricoh driver and the latest OS X/iPhoto. However, I have also heard of a USB problems with OS 10.5.6:
http://developer.apple.com/hardwaredrivers/download/usbdebug.html
At least I have a workaround for now.