Well I managed to find the sourcebook online here; http://www.scribd.com/doc/19470902/d6-Star-Wars-2e-Imperial-Source-Book#scribd
I didn't tell anything new about the backstory of the Empire, as a matter of fact it was almost taken word for word from the AGTTSWU.
But here are some interesting things I've found so far anyway:
(I have by no means read the whole thing, rather I have just skimmed through it looking for something that may seem relevant.)
"The Emperor is a small man, clothed in robes intentionally reminiscent of harmless ascetics on scores of worlds." - p. 12.
I find this kind of interesting as it exclude the idea of robes being specifically 'Jedi uniforms," but it does however suggest why someone like Yoda and Obi-Wan might wear them.
The book also has an entry on an Elite Armor Unit called; Hell's Hammers. The entry starts with;
"Formed during the closing stages of the Clone Wars from armor units of the Old Republic, Hell's Hammers have served the Empire in a large number of actions in the Outer Rim Territories. Used initially to crush opposition to the New Order, Hell's Hammers are now engaged in eradicating Rebel outposts, subjugating planets with Rebel sympathies, and in forcibly bringing reluctant worlds into the Empire." - p. 131.
This isn't much to go on, but it does kind of suggest as pointed out before that the New Order seems to have existed as a political party within the Old Republic for some years prior to the formation of the Empire. Here it might even seem that the New Order was involved in the Clone Wars, possibly even on the same side as the Jedi's at this point.
I was also really surprised to find that there was no entry on Darth Vader. He's barely even mentioned.
This is the only bit I could find that was specifically about him and his role in the Empire;
"The recent setback at the Battle of Yavin has resulted in a few changes to Imperial doctrine. As you are aware,we have lost both the Death Star and its commander, Grand Moff Tarkin. But the doctrine of fear has not been rescinded because of this minor victory for the insignifi-cant rebellion. Instead, the doctrine of fear must be broadened and upgraded. It is time to let that fear spread, time for the Empire to strike back at its enemies and destroy them once and for all. That is why the Emperor has placed his servant, Lord Darth Vader, in command of a special Imperial fleet. This fleet, led by Lord Vader's new Super-class Star Destroyer Executor, has been charged with the mission to hunt down the rebel command base and those rebels that escaped us at Yavin. You are to bow to Lord Vader's wishes as though they were the Emperor's own, extending him every possible assistance he may require in the completion of his task. Soon, nothing will remain to threaten the Emperor's rule." - p. 44.
So I guess Vader was underneath Tarkin in rank during the events of ANH after all. Makes me wonder what he was in the 18 or so years between the formation of the Empire and ANH. Maybe he was more of a henchman as the ANH script suggested, doing whatever dirty work the Emperor needed to be done. It kind of makes sense too. In ANH he's chasing Leia, who at this point is a known as a Rebel leader. He's not leading armies, he's lookin for the Death Star plans. It seems that he's more of a Special Forces commander. He even goes out to fight the Rebel fighters when they attack the Death Star. The book suggests that he didn't gain his role as a General until after the Battle of Yavin.