i know nothing about backing up xbox games. however, you usually can't turn a + writer into a - writer. the cavat being that some burners + only burners have identical hardware to their +/- siblings (and this is the case for some liteon's). in this case you can flash your + only drive into a +/- drive. in order to know if this is possible for your burner, you need to provide the brand and model number of your burner.
also, in order to help you back up your xbox games, forum members are going to need to know what exactly to are trying to do that is not working -- step by step -- and as detailed as possible.
folks around here are miracle workers not mindreaders