I may be wrong here,but cant you convert pokemon into file format and then convert to gen3/4/5 format? I remember seeing something like that...
Doubt it. There were so many changes between the first two gens and the third that I don't see it working.
Even if it was possible, it would require ROM/emulator access and thus couldn't be accomplished on cartridges.
It would definitely be possible to do a "converter program" of sorts, but yes, it would require some way to extract the data and individual Pokemon files from the game. A lot of things would have to be randomized, of course, and you'd probably end up with really terrible current-format Pokemon in the end.
THAT'S MISS FUNERAL CAKE TO YOU i disgust myself and everyone around me
If I carried over, you mean "used multiple times in every generation they were available", then yes.
I had an Espeon and Umbreon dual team that were hatched from the same litter and used in Gen II. Gen III also saw me using the two Pokémon together in a Coliseum team and carrying them over to Gen IV. Then, when I lost the game with them on it, I obtained the two Pokémon by breeding yet again in Gen IV and carried them over to Gen V.
Houndoom, Clefable, and Pidgeot come close, but I skipped a Generation with them (Gens III, II, and IV, respectively).
You know you read too much when you dream about flying books.
Ruby and Sapphire are the furthest back you can go if you want to transfer up through the generations. Canonically, and compatability-wise, Gens 1 and 2 don't exist. At least, not as stand alone generations.