You can try adding the following options to the Virtual Machine's .vmx configuration file.
isolation.tools.copy.disable = "TRUE"
isolation.tools.paste.disable = "TRUE"
Have a look at: Editing the .vmx file for your Fusion virtual machine (1014782)
Note: When editing the .vmx configuration file the Virtual Machine should be shutdown, not suspended and VMware Fusion closed.
Message was edited by: WoodyZ - Forgot to add the boolean value and have now also tested these options under VMware Fusion 5.0.3 on a Windows XP Virtual Machine and these two options will disable Copy and Paste operations between the Host and Guest and vice versa.