do you need public ips in the internal area, too? i guess PIX is another firewall-box, so let's say, you have network cards at positions a - g (internet)a -- b(ASL-box)c -- d(DMZ) - e(PIX)f - g(Internal) with subnets for (a,b); (c,d,e); (f,g) d and g can be more than one machine! so my idea is: a: your providers ip b: your official ip (and aliase for all used ip's in DMZ or private) ASL:
needs NAT rules to translate aliases to private adresses
needs route to private network behind PIX (192.168.2.0, gw 192.168.1.250