genprism.os2 I have is RC4 with a date of 11/01/2004,

Though I managed to get the AIR-PCM350 running with the 340 driver, IBM does not officially support this. IBM has just started the development of another business-only device driver especially for the CISCO 350 PC Card, which will also officially support the CISCO 340 PCMCIA series and that will incorporate LEAP support in the driver package. Development of this driver should be straightforward, since the 350 is a very close follow-on to the 340, since you can even flash a 340 to make it a 350 card. The new 350 driver should also support the miniPCI version of the 350 Series, including bus mastering.
The old IBM driver is unfortunately not stable, testing made it trap after a few seconds of full traffic load. The support for encryption is only for 40 bits (WEP-64), only one key. With the new 350 Beta driver, there is better throughput than any PRISM-based card. This comes due to a different buffer allocation scheme in the driver.