I've finally uploaded my u-boot patch with NAND support. It's at:
http://the.earth.li/pub/e3/2.6.15/u-boot-e3-20060321.diff
with a precompiled image at:
http://the.earth.li/pub/e3/2.6.15/u-boot.bin
It also changes the processor to be the correct 925t rather than 926 based one, but this seems to have slowed down the boot a lot. Also the NAND support is really slow; for some reason I can't get the support for the NAND ready bit (on GPIO 12 I believe) to work, though it seems fine for the kernel.
I haven't had a chance to further look at getting PBL loading u-boot from NAND, but I hope to play over the weekend.
J.