I just discovered that 'system a' has no DvD burner. System B has one. I can drop ilife onto system B, but ... which of the collection of 'import/export' mechanisms makes sense here to use the B drive if the movie is under construction on A? Heck, can I just somewhow share the 'media browser' and just do the DVD part of the process on System B?
Do you mean to import/export the iMovie project (or whatever) from system A to system B?
As mankoff points out you can simply share the DVD drive over the network, or alternatively, once you've got iLife on system B, you could browse to your project file over the network (on system B) and burn that way as well.
Using either of these methods you don't need to do any importing or exporting, so they are probably the two best methods for you.
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.