About a month ago, I made initial port of u-boot bootloader to Palm Tungsten|C. Back then it was bootable from PalmOS and pretty safe to tinker with. But just recently I gave it a go on real hardware. The hardware of choice was an old PalmTC I had lying around here for some time, covered with dust since I thought it was somehow damaged. To my surprise, after a few hours with JTAG ( more info on JTAG with Palm hardware ) and openwince-jtag tool, I managed to get serial console ( for that I used FTDI-based RS-232/USB converter from asix.cz ). Tinkering with it further got me a proper LCD support and MMC support (therefore it's even safe to damage kernel in flash as it still can boot from MMC card if inserted).
The patch is here: http://marex.hackndev.com/uboot/0001-Hacky-PalmTC-support-for-uboot.patch
Just apply it on top of uboot sources, compile and you should be ready to test it, but be careful, writing to flash can damage your device and the only way out is to solder JTAG to the board and reflash using that (the way I did the initial revival process for my PalmTC unit).