Tim,
The YAFFS driver for WinCE will create a folder on your device. The default name of this folder is YaffsPart1. There is a Windows CE driver document on the PXA270 download site, have you looked at this?
http://www.logicpd.com/do...25/1003778_Rev_B.pdf
The PXA270 Card Engine comes in two options, one with NOR Flash and one with NAND FLash. You need to be sure you use the NAND Flash YAFFS driver. (It specifically says 'NAND')
Please read the readme for the driver and the .reg has some good comments on how to configure partitions. (If you are configuring your partitions as mentioned below, make sure you change the .reg file for the driver to match, otherwise it won't work and you could really mess up the NAND Flash)
Also, just fyi, I'd suggest using 'NAND Flash' or 'Flash' instead of EEPROM, it is a little confusing since there is an actual EEPROM on the board.
-Mike