A_M_Swallow
Regular
Not sure about the Walkers of Sigma 957 and the Vorlons. I get the feeling that the Vorlons were rather arrogant, that they resembled the human race in that regard--they reached out too far, too fast (i.e. Thirdspace issues here when they tried to become gods.) I think that's why Kosh had a "thing" for the humans, perhaps they reminded him of his own race so long ago. And, we see that the human race (after much strife and evolving) does eventually become very much like the Vorlons (encounter suit and all.) Though the humans seemed to have retained their solid form in the future, like Lorien's race.
I would wager that the walkers and the vorlons are just two of those "first ones" that never quite got along. =) I'd love to hear other ideas, though, on that one. And I'm not sure that Vorlon technology is neccessarily less "uber" than the First Ones, but you get enough First Ones together and it can certainly take out a Vorlon mother-ship. =)
The Shadows method of forcing evolution is to make the races fight. All the other First Ones were brought up by the Shadows. So all of the First Ones have spent the last 'N' million years fighting each other.