Note: Tested on XP, please report in comments about Vista! Thanks
If you have installed office2003 and office2007 on the same computer you probably get the dialogs below every time they switch between Word 2007 and Word 2003.
The fix to the problem is very simple as it turns out - simply run the following commands (by pressing the Windows Key+R or typing it into the Start/Run command box. Use the line with Office\11.0 if you have Office 2003 installed and Office\12.0 if you have Office 2007 installed. You can use both if you have both installed :
reg add HKCU\Software\Microsoft\Office\11.0\Word\Options /v NoReReg /t REG_DWORD /d 1
reg add HKCU\Software\Microsoft\Office\12.0\Word\Options /v NoReReg /t REG_DWORD /d 1
That is it. Office 2007 might want to have one more spin round the block with it's configuration dialog box, but that should be it.
Comments are welcome