How can I clean up/remove invalid entries from the registry?

A. Microsoft have released a utility called RegClean which will go through your machines registry and delete any unused/unnecessary keys. The current version is 4.1a and however Microsoft have removed it as a download but you may find it on the web via a seatch

Once downloaded just click on the Executable and it will check your registry, once the check is completed you will be given an option to fix errors "Fix Errors" button. You can click the Exit button to exit.

RegClean creates an uninstall file in the directory the image is located in, of the name

"Undo .reg"
e.g. "Undo workstation 19980320 104323.reg"

To undo the changes just double click (or single depending on your config ;-) ) this file.