Since you're using a Mac, you should download the latest version of Palm Desktop for Mac from Palm.com. The version on the Clie CD is for Windows.
Re-install the downloaded Palm Desktop, the re-install MissingSync. Check the MarkSpace web site to make sure you have the latest version (minor updates are free).
To soft reset the Clie, press the reset hole using the stylus. To hard reset it, follow the instructions in the manual which you can access on the Mac since the manual and help files are all cross platform PDF and HTML web pages. Basically you press the power and reset buttons simultanously until the unit asks you if you want to erase everything. I'd reinstall the desktop software before trying to hard reset the PDA though.