First, check your router settings, as stated before. Assure that the signal output is set to "mixed", because if it is not set to mixed, it will be outputting higher signals (e.g. G/N). I am positive that if you do not have a high-end iPAQ, or if you do not have a external network card, you have an internal "B" card.
If this is not the case, I did some digging of my own, try this link here: javascript

penExternal('http://h20000.www2.hp.com/bizsupport/TechSupport/SoftwareDescription.jsp?lang=en&cc=us&prodTypeId=2 15348&prodSeriesId=421399&swItem=ip-46623-1&prodNameId=443063&swEnvOID=2067&swLang=8&taskId= 135&mode=4&idx=0')
I am not sure whether or not this patch resets the ROM or not, so make sure you back up your data before you use this update.
According to the list, Wifi is one the fixes it performs. Although, upon reading further, I cannot see where a hard reset is performed. Good Luck.