When gparted is started using a normal user and setuid:ing to root (via consolehelper), it claims it cannot find any devices. It does however work fine if I use su for the setuid process, so there is something in the consolehelper system that confuses gparted.
This bug appears to have been reported against 'rawhide' during the Fedora 11 development cycle. Changing version to '11'. More information and reason for this action is here: http://fedoraproject.org/wiki/BugZappers/HouseKeeping
I've somehow missed this for a long time, sorry. You shouldn't need to other 'setuid:ing to root' to run gparted. It is already (properly) configured to use consolehelper, just call 'gparted' (or start if from the desktop menu) to run the app.