If you're flashing from onboard the device, instead of running this as root:
You do:
The "-R" is optional in both. It just tells your device to reboot right after flashing. This is somewhat safer because in case your N900 has a battery problem or runs out of power or crashes soon after, it might not be able to actually write the changes to disk. (In Linux, the kernel sometimes waits, keeping changes to disk in memory, instead of writing it to disk immediately. When it reboots, it will write every change not yet made to disk before shutting everything down.) However, if you don't immediately need or want to reboot, you can just run "sync", which does just that - writes all the not-yet-written-to-disc-changes to disk. Then you can rest soundly knowing your flashed kernel is saved, so you can reboot at leisure.

- Edit -

Didn't actually say this first time around so: Thanks for posting this in a single concise how-to. I suspect this information was lying around in various places, but it's always nice to see people making clear instructions.

Also, I haven't tried this one, but I thought I'd point out that e-yes (one of the NITDroid developers) created a patch for uboot that makes it boot the attached kernel if you boot with keyboard closed, and takes you to the normal uboot loader screen with the countdown if you boot with keyboard slid out.
Thread - first post on this page: http://talk.maemo.org/showthread.php?t=64921&page=10
Post itself: http://talk.maemo.org/showpost.php?p...1&postcount=91