You can use Stanza Desktop for PC to do this. This is from the Stanza FAQ page:
Sharing using Stanza Desktop
The dedicated Stanza iPhone application, which can be downloaded onto the iPhone via the Apple App Store, can upload books from your computer using Stanza Desktop. The Stanza Desktop application is currently available for Apple Macintosh and Windows computers from http://download.lexcycle.com.
Launch Stanza Desktop.
Go to File->Open, and open a book or document in one of Stanza's supported formats. Note: The text of eReader books will not be displayed, but you can still use this interface to share books with Stanza iPhone.
Go to the "Tools" menu, and ensure that the "Enable Sharing" menu item is checked.
Ensure that your iPhone is connected to the same wireless network that your PC is on.
Launch Stanza on your iPhone.
From the top-level library menu, select "Shared Books". You should see your computer name. Select it.
Stanza Desktop will then notify you that your iPhone is attempting to connect to your shared library, and request your permission to allow the connection.
Once you have granted permission, Stanza iPhone will display a list of books that are open in Stanza Desktop.
Tap on the book to download it Stanza on your iPhone. It will appear in Titles and Recent Downloads.