Z(in) for small signal analysis with BJT for unbypassed emitter and r0 in place
Let the current through r0 be Ir. Applying KCL,  

1.  Ie = (B*Ib) + Ib + Ir.
2. Io = Ir + (B*Ib).


Applying KVL,

(Io*Rc) + (Ir*r0) + (Ie*Re) = 0.


From eq 2:

Ir = -[(B*Ib*Rc) + Ie*Re]/r0+Rc.

Ie = (1+B)*Ib - [(B*Ib*Rc) + (Ie*Re)]/(r0+Rc).

Ie(1 + (Re/r0+Rc)) = (1+B)Ib - (B*Ib*Rc)/r0+Rc.

Vb = Ib(B*Re) + Ie*Re.  

Vb= Ib(B*Re) + Ib*Re[(B+1) + (Rc/r0)]/[1 + (Rc+Re)/r0]

Zb = B*Re + Re[(b+1) + (Rc/r0)]/[1+(Rc+Re)/r0]


Please pardon me I don't know which software to use for formatting. I tried to upload an image, but it failed. I have skipped some of the steps which could be easily arranged.