Microsoft has posted the syntax for the CAB file installer, WCELOAD.EXE. Take a look at this MSDN post.
Of particular note to ADS developers are the parameters for unattended/silent operation. If you are installing drivers or files from a CAB file at boot, you proably will want to use syntax like the following:
This will not prompt the user for input and will not delete the CAB file when done (the CAB file will be there the next time the system boots).
You'll see that the notes currently posted (30-Nov-2006) are a bit inconsistent (nodelete and silent options from the example aren't defined in the text), but it should get us all moving in the right direction.
To further confuse things there are also the flags /noui and /noaskdest. The availability of these woefully undocumented flags for wceload actually changes across CE versions. For example CE 4.2 and earlier did not support /silent (which I believe was a new addition in 5.0). I'm not sure if /noui or /noaskdest carried forward.
wceload's internal behavior shifted in 5.0 as well. As an example, if you attempt to chain installs together using a wait on the earlier process handle to kick of a subsequent install, you'll likely see failures where you get an infinite hang. The best workarounf I've found is to use the toolhelp APIs to see if the wceload process has exited before continuing.