Finally, I made it to work. It's pretty simple in fact.
I'll give you detailed steps so you can revive your Dockstar :
I've used the following on my Windows XP machine.
Get OpenOCD binaries at
http://www.freddiechopin.info/index.php/en/download/category/4-openocdGet uboot-original-mtd0.kwb at
http://jeff.doozan.com/debian/uboot/uboot-original-mtd0.kwb or build you own using instructions at
http://jeff.doozan.com/debian/uboot/.
Put the uboot file in Programs Files/OpenOCD/0.4.0/
Put dockstar.cfg in Programs Files/OpenOCD/0.4.0/board/ (see attachment)
Open a console and type openocd -f board/dockstar.cfg
Open another console and telnet to localhost 4444 and type :
init
sheevaplug_init
dockstar_reset_cpu
load_image uboot-original-mtd0.kwb 0x800000
resume 0x800200
and voilà you should see the green light.
NB : The attachment contains the configuration file for the dockstar using a wiggler cable. If you're using another cable, please change at the begining of the file the line which begin with "interface" according to your need.
Edit : I've juste one small problem, could someone dump the mtd0 using "nanddump -nf usb/mtd0 /dev/mtd0" please ? As I've "*** Warning - bad CRC or NAND, using default environment" when I restored the backup taken with dd.