I heard about a meego rescue disk. that would allow you to access the partitions directly.

http://wiki.meego.com/ARM/N900/Using_Rescue_Initrd

but if you cant even get to flasher, if might be pointless. and from the link you posted. it seems you don't need to press the U button, I know it doesnt seem like a big deal, but it might just be a little thing.