Well to partially answer my own question. I tried a Belkin F5D6020 ver 2 WiFi card, but the iPronto wouldn't boot up...gets as far as the animated Pronto logo.

Also tried an ELSA AireLancer MC-11 card. This would boot up fine and the iPronto had all its usual WiFi functionality. However it didn't cure the crashing whilst asleep problem. The iPronto stll crashes (clock stops, won't wake up without a reset) anything between 20 minutes and 3 hours since its last usage (as judged by the time the clock stops).

Any further suggestions much appreciated.

Tennant