Anyone has the experience of upgrading Debian from woody to lenny?

Dear all,
My debian system was installed on Sep. 2005.
Now, we've decided to upgrade my present system via apt-get to the latest
stable debian branch.
Our kenel is 2.4.21.
We've encountered the problem upgrading the kernel to 2.6.8.
It seems that apt-get fail to execute the update-initramfs and the box fails
to boot.
I execute the command by hand.
But I haven't rebooted my machine since then.
Hope that the new kernel will work for me.
Is there anything else I should pay special attention to?
Thanks for any attention and reply in advance.

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