iwconfig eth0 txpower 15
iwconfig eth0 txpower 30mW
ought to allow one to adjust the power of one's wifi card.
With pdaXrom, I get
"SET failed on device eth0 : Operation not supported."
with both a Symbol LA-4137 and a D-Link DWL(something) in a C-860. In fairness, I've never used the Symbol with any other ROM... but the D-Link was used quite a bit in a 5500 with OpenZaurus and was perfectly happy to adjust it's power level.
The larger issue is that neither the Symbol or the (hellishly powerful) D-Link detect much of anything with Kismet under pdaXrom. Increasing the txpower traditionally solves this problem - or at least helps.