As i suspected you have mixed your sources.list,in your case Lenny with Unstable.
This is why apt wants to upgrade udev,but can't because you are using the 2.6.26 kernel.
Edit your sources.list to look something like this:
#deb cdrom:[Debian GNU/Linux 5.04 _Lenny_ - Official i386 CD Binary-1]
#deb cdrom:[Debian GNU/Linux 5.04 _Lenny_ - Official i386 CD Binary-2]
deb http://ftp.us.debian.org/debian/ lenny main contrib non-free
deb-src http://ftp.us.debian.org/debian/ lenny main contrib non-free
deb http://security.debian.org/ lenny/updates main contrib non-free
deb-src http://security.debian.org/ lenny/updates main contrib non-free
deb http://volatile.debian.org/debian-volatile lenny/volatile main contrib non-free
Then do an aptitude update && aptitude keep-all
and use aptitude from this point on.
Have you done any updates/upgrades while your sources.list has been pointing to Unstable?.
Looking at the picture saying "588 not upgraded" I'd say probably not.But it's worth checking.
That's why i asked for the output of cat /etc/debian_version
which you still have not posted.