To resolve the problem during the installation od Microsft Dynamics CRM 4.0 Data Migration tool you can set on the registry the path of CRM installation . Follow this steps:
1) Open the registry (regedit)
2) Search the Key: [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Installer\UserData\S-1-5-18\Products\059DD8CB00184F24E99A62CF4D6109FA\InstallProperties]
Value: InstallLocation
3) Set the value: "C:\Program Files\Microsoft Dynamics CRM " and close the registry.
Now the installation well done.
Good programming
Fulvio