My w12 (CF wireless card) used to work with 1.5.6, How ever I needed to reboot everyonce in a while in order to maintain it working. I do not know why, but the w12 make my Z semi-freeze, the screen images startsd for example to desapeard, like vanished. I just needed to eject the w12, an the Z cames to live again.
I believed that was a matter of modile-kernel, since I have a pxa 255, so now I am using watapon 1.5.6 but with the original kernel.
And my Z is working much better. It does not freeze, and thew12 is working better ( is not respoonding as use to do it with the original rom, but almost )
So may be the problem with the 1.5.6 and wireless card only appears in the Z with pxa 255.
Hope this help