  We present a general method to deform the inhomogeneous algebras of the
$B_n,C_n,D_n$ type, and find the corresponding bicovariant differential
calculus. The method is based on a projection from $B_{n+1}, C_{n+1}, D_{n+1}$.
For example we obtain the (bicovariant) inhomogeneous $q$-algebra $ISO_q(N)$ as
a consistent projection of the (bicovariant) $q$-algebra $SO_q(N+2)$. This
projection works for particular multiparametric deformations of $SO(N+2)$, the
so-called ``minimal" deformations. The case of $ISO_q(4)$ is studied in detail:
a real form corresponding to a Lorentz signature exists only for one of the
minimal deformations, depending on one parameter $q$. The quantum Poincar\'e
Lie algebra is given explicitly: it has 10 generators (no dilatations) and
contains the {\sl classical} Lorentz algebra. Only the commutation relations
involving the momenta depend on $q$. Finally, we discuss a $q$-deformation of
gravity based on the ``gauging" of this $q$-Poincar\'e algebra: the lagrangian
generalizes the usual Einstein-Cartan lagrangian.
