OK, I'm going back to my book writing...dunno why, I'm crap at it!!
Anyway, I've an idea where my heroes are back in time, 65 million years-ish 
doing experiments, or some other good enough excuse, on the asteriod that 
hits the Earth and wipes out the dinosaurs (let's assume for know that that 
is what happened).
However, the shuttle that is on the asteriod explodes for some inexplicible 
reason and slightly diverts the asteriod enough to miss the Earth, and hence 
the dinosaurs survive.
So, unaware, our heroes return to their own time (26th century) and find it 
slightly different...I need some ideas on how it may be different. My 
current idea is that (in a similar vein to Planet Of The Apes) the planet is 
ruled by intelligent dinosaurs...i.e. evolved to the level of humans, but as 
they had 65 million years head start, they're a little more advanced.

Cheers,

Gerald.