...um hi again the point i originally wanted to make was this :)
I agree with what someone else said above (sorry im bad with names).
When obi wan says.... jedi were the guardians of peace and justice...before the dark times, before the empire... ie....a longer period of time than 20 years.
In my mind before the PT arrived. I imagined the backstory as thus: The Empire had been in power for a loong time, since before obi wan was born... if people in star wars have relatively the same life span! - The dark times refers to the period of time since the republic fell/crumpled and the time before the empire arrived.
Obi Wan grew up in the time of the empire - then came the clone wars which was an event much like a civil war - when battles were fought possibly by people who wanted freedom on one side versus the empire on the other that had an unlimited number of clone soldiers at its disposal (the thought of droid armies never even crossed my mind).
During the war - Obi wan a soldier who is also a jedi knight, respected by those that have fought with him in his unit. thus is promoted quite fast up the ranks untill becoming a general. But.... generally (no pun intended) jedi knights are not a well known order. They are often misunderstood, disrespected by those that havnt been in direct contact of the force manifestations - it is very rarely that force sensitive people are encountered. Thus Obi wans surprise when he encounters Anakin Skywalker who he senses is also force sensitive. Yoda is an ex-teacher, who doesnt think of himself as anything special but once taught obi wan.
...maybe have yoda in episode 1 but then he makes no other appearance until empire strikes back. The story then follows Obi wan - and his experiances in war as a solider and as a jedi practioner. Who then meets Anakin a brave pilot - the two become friends, Obi wan teaches Anakin all he knows about jedi techniques in order to compliment his pilotting skills as well as infantry type skills - Anakin too rises through the ranks with Obi wan - but where Obi wan remains at peace with his position in the scheme of things... hmm sort of. Anakin becomes disallusioned, and is no longer sure why he is fighting or what the point of it all is for - after seeing comrades die etc.... he starts to use the same tactics that the empire uses, eventually using the force to help him inflict more pain on the enemy soliders/clones.....thus betraying the core belief of the jedi.
Using the force in a state of high emotion allows the force to take control of him, thus losing his grip on reality - he becomes a product of his own hate - the emperoer somehow senses this disturbance in the force - the emperor unknown to anyone else is the last Sith Lord - and realises the potential of Anakin, although the emperor disguises himelf to walk amongst his subjects unknown. He befreinds Anakin as a kind of wild card element that is the opposite of Obi -wan and manipulates anakin.
Obi wan realises that anakin has become "lost to the light" and tries to save anakin from himself, only to agravate him more untill Obi wan is forced to defend himself... they fight......da da da....anakin falls in lava.... the person that survives is darth vader...."the transformation is forever burned into him..." The emperor reveals his true self to anakin they join forces - Anakins betrayal of the free peoples ends the war and he slaughters the rest if the known jedi ......thinking that obi wan is also dead... but anakin and the empire never knew of the existance of Yoda....so what has become of him? ...you find out in episode 5.
You dont see the suit of darth vader before episode 4.....episode 3 ends with anakin skywalker in a hospital type ward being healed...possibly suspended in a bacta tank? ....fade to credits.
no mention of Darth...anyone.
well something like that.