Are you running Windows XP Professional x64 Edition ? And want to install/run Windows CE 5.0 tools on that system? - The tools don't install by default, here's a set of steps to get the installer to work [Note: This is not supported, so you are on your own if this doesn't work].
1. Install the Orca .msi editor
2. Xcopy the whole Windows CE 5.0 CD1 to a directory on your hard drive.
3. Use orca to edit " Microsoft Windows CE 5.0.msi" in the copy of CD1.
4. Navigate to the CustomAction table, then sort by Source column.
5. Delete all entries with source that starts with "CustomDLL".
6. Save the .msi, then run setup.exe from the copy of CD1.