Looking through user media tests in the Blank Media forum, it seems CMC MAG AM3 can be ok, but varies quite a lot. You may have a bad batch of these particular disks.
Another problem might be that these disks do not have good support in the firmware of your drive. The firmware you have now is A113 and the drive itself is made by LG. You can check with LG for newer firmware, but this drive is fairly old now, (I found a review from 2003) and newer disks will often times not work well with older drives. These CMC disks are 16x speed and probably not a good match with your drive.
It doesn’t matter if you are still buying the same brand. Brands change suppliers all the time, and most have moved on to 16x speed disks. Older 8x disks are getting harder to find. For better media, I suggest going to rima.com or supermediastore.com and buying 8x +R Taiyo Yuden. These will be higher quality and a much better match for your drive. I am assuming you are from the US. If not, let us know and other online sites will be suggested.
If you would rather buy locally, I would look for 8x Verbatim if you can still find them. And you should probably think about getting a newer drive. They are about $30 from Newegg these days. Pioneer 115 is a good IDE interface drive.
You can use a free burning program called ImgBurn and change booktype on +R disks. This will make the burned disk look like a commercially made dvd rom disk to your players, and increase compatibility. This only works for +R disks by the way. In ImgBurn look at Tools, Drive, Change Booktype. Then set it for your LG burner. ImgBurn is a very good burning program…I have gone to it entirely for all by dvd video burns. You might want to look through their forum for guides on using it. http://forum.imgburn.com/index.php?showforum=4
I haven’t used the WinDVD program, so I can’t advise you on it, but you don’t need it for backing up dvds. You can use RipIt4Me and compress with DVDShrink. There are guides to using Shrink here at cdfreaks, at mrbass.org and dvdshrink.info And if RipIt4Me fails, you can use DVDFab HD Decrypter. You can learn quite a lot about using these tools here at cdfreaks in the Copy DVD forum.
There are other tools available if you would like to learn about them too. DVDRebuilder is my main compression tool, and though slower than Shrink, the output can be much better.