When in doubt, remove all security. Remove WEP, remove MAC filtering, use a plain SSID, just get it going. As soon as it's working add security features one at a time so you know what's causing the issue. Entering the WEP key can be a pain, and you may want to try the long hex code instead of the passphrase, since some access points do different things if your passphrase is less than the maximum number of characters.

I don't know what level of firmware your iPronto has on it, however early firmware had serious issues with DHCP and it's best to upgrade the firmware as soon as you've got a connection.

To do this, you may find it easier to enter network settings on the iPronto manually, so that you eliminate DHCP altogether (just copy most of the settings from another of your DHCP assigned devices, and use an unused IP - for instance if your IP pool starts at 192.168.1.100 then you can give the iPronto 192.168.1.50 safely).