Funny thing is, copperball, the Tapani sourcebooks mention such an "anti-Imperial terrorist group", but they're not Alliance . ;-) WOTC's Revised-d20 "Dark Forces Saga" write-ups included a mention that Jan Ors (the namesake of the group's initials) was brought into the group but left it.
I don't want to ruin the game for anyone but I've been reading through the d6 version of the rebel alliance sourcebook and it struck me that the rebel group listed in there needs very little done to turn them from the Rebel Alliance we've seen in the movies into an actual terrorist group.
So assuming your group wants to play Imperials it doesn't take much to set up a rogue group of Rebels who are exactly what the Empire describes, its only later on as your game progresses that you reveal that these are a minority and their Empire is far from the benevolent protector its supposed to be.
I always wondered why Palpatine was so xenophobic as the prequels all demonstrated he was more than capable of manipulating them and it felt strange that once he was in charge he made a complete fumble from that point on.
Now what if Palpatine was innocent and that he was just possessed by Darth Sidious as the final stage of his plan, the Anakin we saw at the end of Revenge of the Sith is actually a clone formed from the hand he lost as the end of Attack of the Clones and Kenobi did kill who he thought was Anakin and the true Anakin is locked in that suit to hide the true duplicity and is led to believe Obi-Wan killed Padme...
A bit of facial reconstruction and the use of Sith Alchemy to reinforce his turn to the Darkside and then set him loose explaining the Jedi made a failed coup attempt and are out there preparing the next wave of attacks and need to be stopped of course he could bring them in for questioning...
Ooh you realise that hand Anakin lost would be a great way to have Darth Vader turn up again in the next trilogy, don't you?!
Sorry wrong thread but still if they could do that to Luke's lost hand...
I've tended to wonder what would have happen had Obi-Wan tried a different "truth from a certain point of view"... in the form of telling Luke before Bespin that up until Anakin's "death" Darth Vader had been a noncorporeal entity, but that Vader (and Sidious) then decided as their idea of a sick 'joke' to use the body/"corpse" of the great Jedi as the physical manifestation through which they could purge the Jedi.