Ok first thing.... DO NOT USE XISO!!! What a load of ******* ****!!! It creates truely poor Xbox ISO's and should never been used not even in a blind drunken state.
All you need to do is FTP into the xbox and drag the contents of the D:\ to your PC.
Get ISOCraxtion 3.1 (latest - google for it) and use the non-MS copywritten coded tool to create the xbox format Iso or get hold of GDFimage and use that inconjuction with ISOCraxtion.
There are plenty of other ways to max a DVD backup but I find that the proven method works.
After you have made your image (or multi imaged disc) you can burn it using any burning app. It will burn the ISO in the true xbox format and you should have no problems reading it.