gi is the global image format - it' s definitively used by Primo DVD, so if you have a DVD-R you can burn the image right away.
If not there is still hope: Usually GI's come in a couple of large chunks (two or three) named filename(11).gi and filename(12).gi etc.
Just cat(1) them together (or use copy file(11).gi + file(12).gi file.iso) and you will get an image that ireadable by xISO