You have two options for flashing a kernel. From a Linux host, follow the instructions at http://wiki.maemo.org/Flasher There's a link to the flasher-3.0 tool embedded in the instructions, but it's http://tablets-dev.nokia.com/d3.php if you just want to get flashing

If you want to flash from the tablet itself, you must be running diablo. Use the `fiasco-flasher' tool from a root shell, but be warned that I don't know a way to enable R&D mode using this tool. Without R&D mode your tablet will reboot every 5 minutes or so, and I think you'll want to find a Linux host to reflash the kernel about 5 min after Android boots the first time!