There are outlook express recovery tools available for download on the net, you have to search. I found a microsoft article that mentions corruption of your inbox due to anti-virus scanning software. The article states:
DBXtract is a recovery tool that you can use to restore corrupted Outlook Express e-mail folders. Other recovery utilites are also available. For a complete list of the available tools, visit the following Web site:
The .DBX files are the files relating to Outlook Express mail and if you still have these files somewhere I believe you should be able to copy them to the new install folder.
If you have deleted these files, you may have to try a recovery tool.