Creatspace wants Video and Audio TS in the root directory of the file I send to them. 

The problem is that when I check the dvd (by right clicking, then choosing "explore") the only file that comes up is Video TS.  I can't find the Audio TS file.

Does anyone know what I'm doing wrong?

My workflow is as follows.  While in Avid MC 5, I choose "Send to", DVD Authoring then click OK.  AVID DVD by Sonic than activates. I then build the project and burn an image.  I then burn the DVD using the ISO file.

The Audio TS folder will only have any contents if you make an Audio Hifi DVD. So for normal DVDs the Audio TS folder will be empty. Most applications don't bother to make a folder that has no contents.

The strict DVD spec requires the folder be there and if need be is empty but so many DVDs are created without the folder present it's the norm not to see the folder.

If you have to have it you could use your current DVD as the source for a new DVD and manually add an Audio TS folder to the burn.

But I suspect they don't actually need it (despite what they say)

I haven't done any DVDs recently, but in the past I've never had a rejection for not supplying AUDIO_TS even though the replicator has specified it.  The most I've ever received is a reminder email, but the project still went ahead.  If in doubt contact them, but it's probably just simpler to create the folder manually and say nothing.