First, you should be saving your project as a caproj, not a capx. Caproj allows you to edit an "open" project, with all its animations and event sheets laid out inside a folder, instead of being bound up in a single file.
This way you can freely edit, load up and adjust sprites while another person works on an event sheet, and I think you can work on two separate event sheets at the same time, since these are stored as separate xml files. This way you could, for example, have one person working on the main events of a game while another person builds new levels that each have their own simplified event sheets and call in the main sheet.
I anyone else has any tips on this I'd also love to hear them. I'm gearing up to work with a colleague for Ludum Dare 26.