The config of the PIX seems fine, and the fact that traffic is possible between the desired endpoints indicates NAT is happening as it should. This sounds more like a name resolution issue. Some web servers insist on being able to resolve incoming addresses to a name, so it's possible the DMZ server just can't resolve the 172.30 addresses and that's causing the problem. It's usually possible on most systems to just put an entry in the appropriate "hosts" file as test. So, if you have a user at 172.30.x.y who can do some testing for you, put an entry in the local "hosts" file that assigns a name to that 172.30.x.y address (it doesn't matter what the name is). If that fixes the problem for that user, then you know you have a name resolution issue and you can then pursue the appropriate fix (e.g. DNS, WINS, etc.). If it doesn't fix the problem, then you need to keep looking for the cause, but at least you know one thing that it isn't.
Good luck!
