See the link in my sig for upgrade/downgrade procedure>
Also, I echo Tae's question, are you using DM 4.7 to do your OS installs? If you are, I would strongly suggest you remove DM 4.7 from your computer using Control Panel's Add/Remove Programs, download and install DM 4.6 and try reloading OS 4.5 again before you downgrade to 4.2