What is it you need to know, if you have a backup on a +R disk then just use any diskcopy program and put it on a -R disk. You are only transferring data from one disk to another whether it is +/- does not matter. Use DVD Decrypter in iso read and then use iso write mode and open your MDS file and burn.
@snakero.........http://www.cdfreaks.com/print/article/113 good article about which disk is better, +Rs compared to -Rs. You can not convert a +R to a -R disk! and after you read that article then you can read more in this thread: http://forums.afterdawn.com/thread_view.cfm/183136 #12 also is good reading about +Rs and -Rs and what the differences are!
if you are talking about booktyping your disk I've found none better than imgburn of course your drive will have to support this feature. just click on the little book icon in the lower right hand corner of the main display and select your drive and it will guide you through the rest.