Adding Adjustment Layer CS1

Anybody know how to make one or using these I can’t find any reference in the dictionary or manual. My script currently saves a .psd’s to one location and a bunch of re-sized .jpg’s to other locations at 400pix, 200pix & 100pix. The psd files are kept so if we are not happy with any of the resulting .jpg’s we can manually return to correct the layered .psd’s for this I would like the adjustments to be made as layer adjustments this makes for easier re-tweaking. I am fairly new to scripting but can find no reference to this at all. Even when creating these layers in a existing file the getting the layer properties I can see {kind:Levels Layer} which is happy to compile as a property, but just does not work. Do I need to use the GUI for this if so how I have tried but never done this bit before. Many thanks.