Hello. I've been watching xith since some time ago, and I'm already using it on some simple projects. But I wanna make something BIG!!!
Well, we have some secret fans

Something big ? Good idea.
So, I'm starting this project: A complete Sonic fangame, entirely made with Xith3D.
Oh great so I'm not the only one here to be keen on Sonic ? Great !
But I need some help:
Oh sure.
1> Where can I find a GOOD (and free) BSP map editor?
I would have advised you to use GtkRadiant but you were quicker than me.
2> Is the COLLADA support ready (or working)?
The skeletal animation support is a work-in-progress, coming very soon, thanks to maguila and myself. Static models are loaded okay, as long as they're "triangles", not "polygons". So you can concentrate on animations later, for now get your physics right.
3> What about physics (XPAL)?
We're doing well, thank you

Development is done as requests come so just ask, and you'll see
4> Is it possible to create a kind of texture repository (with texture locator) and "plug" this locator on the model loaders?
The model loaders will usually expect to find textures in the base directory (e.g. parent directory/URL) of the model.
5> There was any performance upgrade after the 0.9b2 release?
Performance is always increasing.
Good luck ! Enjoy Xith3D !