I have a wireless Airport Extreme on Vlan3. My problem is that I can't get internet access from a wireless client which connects to the Airport which is on the DMZ. From my laptop which is connected to the Airport, I can ping the 5505. That's as far as I get.
I was about to prepare a detailed reply to this thread, but I remembered that one of our members has created an excellent tutorial - introduction to the ASA 5500 Firewall which I believe will cover your issues.
Please visit the following link and read through it as I am sure it will provide all the necessary information to get your ASA 5505 working as required.