According to a customer advisory, the H5400 is currently not working with 802.11g access points:
The iPAQ Pocket PC h5400 Series integrated WLAN module will not connect with a WLAN Access Point that supports both 802.11b and 802.11g.
The integrated WLAN module inside your iPAQ Pocket PC allows connections up to 11 mbps (802.11b), but not higher. The technology associated with 802.11g allows for connection throughput higher than 11mbps.
You may notice that the Access Point ID field in the WLAN Status window will alternate between Scanning/Joining/Authenticating in an endless loop and never establish a connection.
HP is developing a WLAN Firmware Upgrade that will allow your iPAQ Pocket PC h5400 Series to connect with a dual (802.11b & 802.11g) WLAN Access Point using the 802.11b technology. This Customer Advisory will be updated when the firmware is available for download as a SoftPaq.
Cheers ~ Arne
Related Links : [More Information] Original Source : [David Hettel - MVP]