I need to split my vista image thats over 4GB into any number of parts but it must be able to install, kinda like so:
user boots 1st DVD/CD
set up install, it starts installing
they insert next disk
install continues
etc
etc


any help would be greatly appreciated!!!

As Vista comes in a dvd fashion don't think it's gunna work for you in that case. But I may be wrong...

They also released Vista in a 6 cd set iirc. So it can be done. I do not know how though unfortunately.

Would a dual layer work?

I have not tried this as anything over the size of a DVD I put on and external drive of some kind (usb thumb or hard drive). That having been said you can use imagex with the split switch to split the WIM that you are putting on the DVD(s) be sure the first segment will be small enough to fit on the first dvd with whatever else may be there with it.