Yeah, the Eldar where definatly a creation of the Old Ones. I don't remember where I read this, but they and the Orks were made to fight the C'tan (I guess they're always making new primitive armies to fight super advanced ones

). The Eldar started out as primitive but they could compete because they had awsome psychic powers, which was the C'tans greatest weakness. Also their emotions created Gods in the Warp that helped too (Khaine, Vaul, etc. This was pre-pantheon). Then the war created the enslavers (chaos as we know it. Since the Old Ones had no emotions the Warp was pretty calm before this point) which broke into the materium via the Eldar psykers and forced the C'tan into hiding, and by that time the Old Ones where beaten into obscurity. I'm not sure 40k really does tie in though, since if the fantasy Orcs where the same ones as the 40k Orks, they would be able to construct things like machine guns and moter vehicles based on instinct. But the fact that he Old One's had an intergalactic empire in both does make for a compelling argument. But then there's the fact that the Elves have the same gods as the Eldar, but they don't seem to have anything else in common, exept a few other parallels that seem to be coincidence. I do kind of like the idea that Sigmar was one of the Lost primarchs

. But then again, the Emperor did discover all of the Primarchs... And didn't Sigmar disapear into the Chaos wastes? Maybe they found him corupted, and that's why he was lost, sort of a tragic figure like Horus... Speculation is fun