I found this on another forum
hope it helps.
"Outlook Express could not be started as MSDE.DLL could not be loaded." Error! I Searched for this file. Nowhere on my computer?
In Control Panel, Add/Remove Programs, is the tab Windows Setup(Components). You'll find Addresses has been unchecked.
(Took me miserable hours to find this). But rechecking and apply alone doesn't do it. You'd think it would. That's where the advice given to Ove's Oct. 29/02. (#684), problem is correct. Simply download as if to install (IE and OE), then custom install only OE, and it will tell you you've got it already. This'll take you to Resume Install and the missing files will download. Or Uninstall OE and/orIE completly, and Reinstall. The missing MSDE.DLL is in Addresses /Windows SetUp.