These instructions used ltib-imx27ads-20071219.
First, get u-boot v2.0:
git clone http://git.denx.de/u-boot-v2.git u-boot-v2
Enter the U-Boot directory:
cd u-boot-v2
Export the proper compilation paths and environment variables:
export ARCH=arm
export PATH="$PATH:/opt/freescale/usr/local/gcc-4.1.2-glibc-2.5-nptl-3/arm-none-linux-gnueabi/bin/"
export CROSS_COMPILE=arm-none-linux-gnueabi-
Configure it for the i.MX27ADS board:
make mx27ads_defconfig
You may want to enable the FEC driver:
make menuconfig
And go to Drivers -> Network drivers and select Yes on i.MX FEC Ethernet driver
Exit the config menu (don't forget to save the configuration) and just make it:
make
Or if you prefer the verbose mode
make V=1
After a quick build, you should get a uboot.bin on your current directory. I used the ADS Toolkit to program the NOR flash.