[Mauzen]

There are loads of them, i prefer using a fast plugin-based.
But this one should do its job too

pawn Код:

stock Float:PointToPoint(Float:x, Float:y, Float:z, Float:xx, Float:yy, Float:zz)
{
    return floatsqroot( (x - xx) * (x - xx) + (y - yy) * (y - yy) + (z - zz) * (z - zz) );
}

(untested)