Don't know anything about transferring .img or similar files to Windows for burning. But the the video_ts and audio-ts folders should be all you need. Those get created along with the .img image during build/format. Even when you burn directly out of DVD-SP, the video and audio-ts folders are created. You should be able to use those on Windows to burn a video DVD with Nero or similar.
Burn speed: I don't like the fact that DVD-SP doesn't allow you to control the burn speed, either. Toast and Describle (version 6 anyway) allow burn speed control. I always burn at 4x. I've found that full DVDs (close to the 4.3GB max) sometimes have problems on players near the end of the show. I also use professional grade DVD-R media: Taiyo Yuden form DiskMakers or Primera. I've been using Watershield printable media for some time with only about 2 failures in hundreds of disks.
Another question: on your Mac, is your DVD burner qualified for 16x burning? Some iMacs and Mac laptops only allow up to 8x burning. Using 16x media on a 8x burner can cause problems, sometimes problems damaging to the burner itself.
Here's the text from my Primera Watershield (Taiyo Yuden):
"This product is not suitable for use with DVD-R/RW drives which do not comply with the new DVD-R specifications for 16x writing speed. Please check your DVD-R/RW drive before using this product. Any use with such non-complying drives may result in loss of data and/or malfunction and damages to the drives. For furthers information concerning necessary actions forr such non-complying drives, please refer to the following web site:
http://www.dvdhs.com"
(Note: that web site does not exist)
Eddie O
Message was edited by: Edward A. Oates