It would help to know WHICH email client you're using, Postdog!!!
If you're using Outlook Express, for example, you'll need to copy all of the files with a .dbx extension (such as inbox.dbx) onto a USB drive (or similar) and then, when you've got Outlook Express going again, replace the 'new' (empty) .dbx files with the old ones.
However if you're using Outlook (rather than Outlook Express) it will be .pst files that you need to do the same with.
Thunderbird, Windows Live Mail, Eudora, etc, will all have their own file formats, so which one is it?