Error on debian lenny when updating Virtualbox 1.x to 3.x

I’m running debian lenny that was setup from minimal netinst. I had installed virtualbox from lenny repos (http://packages.debian.org/lenny/virtualbox-ose). But then I thought of upgrading to newer version of virtualbox because virtualbox 1.x refused to capture my mouse pointer inside guest OS. So, I added lenny-backports repos (http://packages.debian.org/lenny-backports/) to my /etc/apt/sources.list and did ‘sudo apt-get install -t lenny-backports virtualbox). Then when I started virtualbox 3.x, and tried starting (/booting) any guest OS, I got this error:

When I was installing Virtuabox from lenny-backports, the ‘apt-get install’ output was:
http://codepad.org/bjDDof4p
Lines number 90,91,92 and 108, 109, 110, 111, 112 are worth noting in that paste.
(Note: If you want to check out log of output from ‘apt-get install’ on debian, goto /var/log/apt/ and open term.log in your text editor as root)

I then tried finding some help on #debian at irc.freenode.net.
User ‘qq-‘ there suggested that I try rebooting. When I rebooted, I got this message in debian boot messages scrollback:

Starting Virtualbox kernel modules. No suitable vboxnetflt module for running kernel found. Failed

After some discussion, users ‘qq-‘ and ‘jpinx-eeepc’ suggested that I try installing linux-image-2.6.32-bpo.5-686 (you can see mentions of this linux kernel version in the paste linked above). So, I did ‘sudo apt-get install -t lenny-backports linux-image-2.6.32-bpo.5-686’.
When I started Virtualbox this time……wooohooo NO ERRORS THIS TIME 😀

So, in short, install the latest/stable/recommended linux kernel version if you get a similar error.