Massive spoilers in SFX magazine #174

Apparently the situation was that the original Cylons were created on Kobol to serve the humans there, 4,000+ years ago, and evolved a humanoid faction like the later Cylons. There was a war that partially devastated the planet, splintering the people into twelve factions or colonies, plus the Cylons as the thirteenth (it's unclear if this was an intercine human war or another robotic rebellion). The Cylons took off into space on their own, but it seems they were on better terms with the humans of the other colonies and left messages for them. The Cylons went and set up home on another planet: Earth. The other humans later left Kobol and went to settle the Twelve Colonies and all contact was lost. The Cylons of Earth built up a civilisation there, but fell into warfare of their own and devastated the planet some decades ago. At least four survived (he doesn't bring the fifth up at all) and travelled to the Twelve Colonies to find out why humans and their creations have this self-destructive streak to them. They 'switched off' their Cylon sides (with a failsafe that they would 'wake up' if they got close to Earth again) and went to live amongst the humans. Apparently the Final Five are very interested in the Cycle of Time and believed they could better understand it by becoming human.

No explanation is given for how three of them ended up on Galactica and the fourth on Caprica as one of the handful of survivors. No explanation is given for how the modern Cylons have myths and legends about the Final Five (although a logical exrapolation is that the FF were involved in the creation of this generation of Cylons, or perhaps their programming). No explanation is given for the large age gap between Tigh and Tory/Anders/Tyrol either. There is also no confirmation that the Earth in the show is 'our' Earth, a parallel reality Earth or whatever. My guess is that no relationship will be shown between the real world and Earth in the show: it will be left vague, with the possibility that Earth in the show is our world many, many thousands of years into the futuere after humans have left Earth, gone to Kobol etc.