For example with Vista Tool if somebody has a version of Vista that can use ALL of muiz's update packs (update pack, ultimate extras, MCE, etc) plus all of the vista driver packs - you get an install.wim that is over 4GB even when slimmed down to just one version inside (using VLite). The built in ISO maker of Vista Tools can not work with any file bigger than 4GB and the result is no ISO created. No error is given or logged other than a half second DOS window flashing.
I sluethed around and discovered there is a command (Imagex /Split) in the WAIK tools to divide up your install.wim into multiple files for file size compatibility and this finally gets my 7GB ISO to work when installing.
So it would be nice if these front end GUIs that make calls to WAIK could utilize this command.

The latest WAIK has its own ISO builder tool updated supposedly to fix the >4GB issue but I have not seen a documented success posted yet.
I've been re-reading constantly the unattended vista guide posted here http://firegeier.unattended-sponsor.de/en/sitemap.html as this IMO is the only thorough guide on unattended vista out there. The guide is great in that it helps me understand what these Vista front end tools are actually trying to do and fills in the gaps where I wish there was more supplied documentation.