Microsoft keep omega 13 builds very secret. What are the informations we currently have about those builds?

3790.1232: A hybrid of Windows XP Pro and Server 2003
5001: Similar to the build above, but has the Bliss wallpaper with a Longhorn cattle on it, and XP branding gets replaced with LH

Go to the BA Wiki, go to the Vista section and see for yourself.

5019 is referenced in 5048's setup.

AFAIK the only "Omega-13" leaked build is 5.2.3790.1232, which is a Professional build of Server 2003 SP1 RC (basically Windows XP powered by the newer 5.2 kernel instead of 5.1).
More info here and here

I really wish 5019 got leaked someday. I'm still curious as to how it looked. However, from what I've heard, it getting leaked is unlikely...

Not to mention the various 5000 builds, some of them were actually compiled earlier than 3790.1232 and 4093. The 408x builds were when most of the features began to get removed, so the reset may have been planned as early as May-June 2004, but who knows right. I have a screenshot of 5000 somewhere, but it's confirmed fake.

I know only 3790.1232 (it's almost Windows XP with very, very small changes.)