Moving an iMovie-11 'work in progress' moving from one system to another
Accessing DVD drives

Under System Preferences > Sharing you can share the DVD drive of B with A.

This should allow you to use the DVD burner on B as though it were a part of A, so you can just keep working on A.

Import / Export

You mention iLife, but not what program in iLife you are using, nor what you are doing with that program, so it is difficult to suggest an export/import method.

Moving 'Work in Progress'

Your question is about accessing a DVD drive, but your title is more generic. 

If you want to move work in progress between two computers, you can use a variety of techniques, including, for example, DropBox, USB drives, shared folders over wireless or wired intranet or internet, etc.