In all my other games I had never a problem when I entered Nipton:

1) The guy who was attacked by his gf runs up to me and gives me his caps after a speech check
2) The "winner" of the lottery spawns and yells at me, what a lucky guy he is
3) When I approach the townhall, Vulpes Inculta starts explainig me his reasons to slaughter all the people and gives me the quest "cold cold heart"

In my current game only the events with the caps-guy are normal. Anything else won't happen.

No "winner" and no Vulpes. His men and his hounds were present, though.
When I search the city hall I find anything, which I found in former games, but I can't complete the quest for Ranger Ghost.

I have naby saves, so I loaded one afer the other, ending up several hours of gameplay before Nipton, but nothing changed. The last save I reloaded was one of Primm, when I cleared the jail. Before that
I was in the starting town, so I guess, in this game something prevented certain events to spawn by "default".

I disabled all mods, which I didn't have in games, where the events happened. No success.

I searched for a console command to spawn Vulpes, but found none except player.placeatme XY, which did not work with the refID for Vulpes I found in the Wiki.

Now I won't whine about one broken quest. I'm just afraid, that this will happen with other relevant NPCs, too.

Any idea about what's going on?

maybe mods screwed up your game... it is possible some of the effects don't go away until you start a new game or load a save before you enabled the mods. that seems like the only plausible explanation for me... maybe if you give us a list of your mods it could help.

omg, I use MANY mods , most of them are just custom armour and clothing stuff. As I wrote, I disabled all mods, which I did not use in previous games - so I agree, it could be one of the newer ones, which screws up the game.

The newer ones are:
1) Miria, a custom companion
2) Centered 3rd person camera
3) SOG Fusion Tomahawk
4) XM8 Assault Rifle
5) Portable tent (does not work, not enabled)
6) Companion de-equip (no more Veronica's hood!)
7) AfricanAmericanAAlbino (because of nice outfits)
8) d3d9.dll (ATI-fix)

That's it.
I'm neither a modder nor do I know much about programming and scripting. But nevertheless, why should a mod which comes with some textures and meshes screw up a game? So IMO the weapons-, armour- and clothing stuff as well as so called "replacers" cannot be the cause, because they change only grafic stuff.
But a custom NPC and direct manipulation of engine-related stuff like the .dll and the camera.... I suspect that's the way to search for such bugs, right?

Oh well, the game itself has even unmodded so many bugs and glitches... I guess, it'll be some hard work to figure out, what causes what, right?
<_<

Did you already go to vegas? I'm pretty sure vulpas is also the guy who talks to you and delivers ceasars message, so if you went to vegas you might have changed the nipton experience.

Nah, not with this character. I just started her, did Primm and visited Mojave Outpost.

Ok, sorry for double post, but I found out, what causes the trouble:
It's one of these unlimited companion mods (not sure if it would be fair to post here which one).

I saved a game near Nipton. Then I un- and reinstalled the game, started it with no mod avctive.
The NPCs spawned. I quit, checked one mod, reloaded the old save - NPCs spawned.
When I finally loaded this "unlimited comp. mod" the NPCs did not spawn.
Quit, unchecked it and checked all other mods: NPCs spawned.
Quit, checked suspicious mod, too: No NPCs.

I guess, this is kinda evidence, that said mod makes trouble, right?

It says Modder not looking at doing things the right way cause trouble.