Well, I figured out a workaround answer to my own question. Seems like there should be an easier way, but this works. After creating an album of selected photos, take one more photo with the camera. Then, load that one photo into Picasa, which will create a new folder. Select all the photos within the album and drag them into the newly-created folder. Delete the photo that was taken just to create the folder, and voila! The album has been converted to a folder that can be selected while syncing the iPhone.