So, I'd like to know if there is any effect that simulates these little jumps that we see inherent to film projection.

This "little jumps" are specially noticeable when subjets are NOT in motion. That is, when static credits appear, static establishing shots, etc...

Thanks all for the help,

There used to be a script called "Vegas Quake" that probably would have done the job for you.
Unfortunately it was written for an older version of Vegas Pro and never updated.
Take a look at NewBlue Film Effects (http://www.newbluefx.com/film-effects.html) as it seems to have what you want.
The $100 price tag may be a bit much though :-(

Just let me clarify:

There is a JITTER effect in vegas. But I think this is not what I am looking for.
Vegas' jitter effect is not constant and changes in amplitude too much (when I say amplitude I mean the movement)

I am looking for a more consistent, low-amplitude "jitter" effect.

Yep, NewBlue has exactly what you want. They have a large number of different effects in the Film Effects plugin.

In the Video FX selections there is one called Film Effects. Within that you can select which attributes of a film effect you'd like. The effect Jitter" is the one that causes the little jumps. You can select how much or how little of each effect you'd like to use.

Never mind you found it.

Hmmm... I'd get the film projector or camera checked if there was jitter, there's obviously a fault, otherwise you're running badly worn print with splices. Those tend to be more noticeable on the smaller film gauges, you can hear all your cuts on 8mm.

This error in a film projector, a film printer, or a film camera, is called gate weave.

Usually, it is so small that it isn't really noticeable when looking at people or real objects, but, we expect titles to be rock solid, and sometimes they aren't.

The big jumps might be from torn sprocket holes on a really old print, or, the wearing of mechanical parts in an old projector.