How can I clear the Run history?

Start the registry editor (regedit.exe)

Move to HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionExplorerRunMRU

Select the entry you wish to remove, e.g. h

Press the Del key (or select Edit - Delete) and click Yes to the confirmation

Double click the MRUList value and remove the letter you just deleted. Click OK to save the change

Close the registry editor

Start the TweakUI control panel applet (Start - Settings - Control Panel - TweakUI)

Click the Paranoia tab :-)

Check the "Clear Run history at logon"

Click the "Clear Selected Items Now"

You can then either clear the check on "Clear Run history at logon" and click OK or leave it checked to automatically clear the Run at logon