Irongeek- I think it depends on how the endpoint is configured. For instance, if you have you 802.11g setup to only broadcast in 802.11g I don't think the 802.11B network card would pick up any traffic. Mainly because the 802.11b card cannot pick up the modulation from the 802.11g end point. 802.11b can't recognize ODFM modulation. Only DSSS and CKK modulation can be received.

So if your 802.11g endpoint and card had to handshake their way down into the sub 11Mb/sec speed range then I guess it could be possible to pickup a signal as even 802.11g uses the same modulation as 802.11b when the speed is 1,2, 5, or 11 Mb/sec where DSSS, and CCK is used for signaling.

Even then I have to wonder because 802.11g uses what the standard calls ERP-OFDM, ERP-PBCC, DSSS-OFDM, ERP-DSSS/CCK. So the standard DSSS and CCK has been extended beyond what 802.11b had. 802.11g is called extended rate signaling, 802.11b has high rate signaling.

It is described in clause 18 and 19 of the official IEEE 802.11g standard.