Hi James - We just got done doing the same. We had a Checkpoint 4.1 firewall and put in a PIX515e firewall. Everything went fine except for two problems. The major problem that we had and I'm sure you wont have this issue is the internet (cisco2501) router was breaking arp entries so some of our web sites were not working from time to time, In our infinit wisdom we decided to statically assign the arp table entries at that router and forgot about it. When we put in the new firewall these entries caused us some problems until we changes them to the mac address of the new firewall. Yes they are still in there. The other issue we had was that the PIX came loaded with v6.1 and that was a problem (we found out after we were up and using the pix) because we use a websense url filtering server and the websense/pixv6.1 do not play well together. So, If your using websense I would upgrade the pix to the latest ios if it doesnt come loaded with it. I'm still a little hurt that Cisco sent us a firewall with an old os but I'm getting over it because the thing works so well. We really are happy with it and after we got through some sticky situations it has worked vary well for two months now. Dont forget to turn off the router before you switch over, or at least clear the arp table once you hookup the new firewall.
