Ok, let's see if we can help you out.
(bytheway, I don't see why you're using two PIX's, but I guesss you use one of the other interfaces on PIX A for hosting or something)
You didn't provide the global outside address which you wanted to use, so, I will put in where you shoul fill in this gap.
I will assume you want the server to be reachable from Internet using HTTP (TCP port 80). If more protocols needed, you can simply add the appropiate access-list statements to the same outside-in access-list.
PIX A
static (pixzone, outside) 192.168.100.100 netmask
255.255.255.255
route pixzone 192.168.100.0 255.255.255.0 192.168.4.2
route outside 0.0.0.0 0.0.0.0
access-list outside-in permit tcp any host eq 80
access-group outside-in in interface outside
PIX B
static (inside, pixzone) 192.168.100.100 192.168.100.100 netmask
255.255.255.255
*remember that the address is allready translated as it arrives at PIX B*
route pixzone 0.0.0.0 0.0.0.0
access-list pixzone-in permit tcp any host 192.168.100.100 eq 80
access-group pixzone in interface pixzone
Off course this is not all, but the rest will depend on other things needed, like dynamic routing, ip verify (to prevent spoofing), how the rest of your design is, et cetera, but I hope this helps.
Regards,
Leo