Chancellor Palapatine (sp) said in Episode 2 that the Republic had stood for a thousand years
He did, but Obi-Wan in SW4 said that the Jedi protected the Republic for over a thousand
generations...who to trust?
That appears to have been obliquely addressed in TCW when the black bladed lightsaber was said to have been taken from the temple by the Mandalorians during "the Old Republic", indicating that if not the actual event, something along the lines of the EU's Ruusan reformation is indeed canon.
This also seems to figure into Palpatines "once more the Sith will rule the galaxy" line from RotS as well as mentions of the Old Sith Empire in the TCW's slaver arc. Then there's Windu's line: "the oppression of the Sith will never return."
All of which seem to indicate that the Republic fell and the Sith rule for a time (perhaps even centuries) until their own infighting weakened them enough for (presumably) the Jedi to lead an uprising and (almost) wipe them out.
Small addendum: Ki Adi Mundi also stated that "the Sith have been extinct for a millennium."