Should be able to. .EML files are ordinary text files in the standard format for emails. They are independent of the mail client being used.
Just transfer them across and drop them in the folder where the Win8 ones are kept, e.g. Store Folder
\Local Folders\Inbox. You can even drag them into the folders of WM itself when it it is running.
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 20 Meg WBC