.gi's are sort of like a bin/cue or ISO/MDS set. Seems to me there was a guide out there somewhere for converting it to .bin/.cue or something--but it has been like two years since I looked into it. You can still find the original Primo release of the RNM engine out there that will work with some of the older burners with the newer pxengine updates. This is the "legit" way to have a free app to burn the .gi's. If you know someone who had an older Pioneer drive, you could possibly make a deal for their older RNDX that was packed in with their drive if they don't use the proggie anymore. Then you could legitimately upgrade to RNM 4.50 from there and install the 5.07 px engine.
A lot of effort for this problem no matter how you look at it. The best thing to do is to recreate the image in an app you already have, or with the freely distributed DVDDecrypter. If you don't have a means of recreating the image from a source disc, then please do not pursure this any further here. Go back and read the rules.
If it ain't broke don't try to fix it! But, hell if you can tweak that bastard just a little bit more....hehehe.