I'm also having trouble installing the latest kernel 2.6.30 stable on Ubuntu 9.04.  The deb's I tried installing I got from "http://kernel.ubuntu.com/~kernel-ppa/mainline/v2.6.30".  Technically the kernel installs fine.  It's the nvidia modules it seems to have problems with.  All other kernels I've downloaded and installed from that site have worked perfectly with nvidia drivers.  It's this latest kernel that is the first to not work.

Here's the output I got in shell.

$ sudo dpkg -i linux*2.6.30*.deb
Selecting previously deselected package linux-headers-2.6.30-020630.
(Reading database ... 173270 files and directories currently installed.)
Unpacking linux-headers-2.6.30-020630 (from linux-headers-2.6.30-020630_2.6.30-020630_all.deb) ...
Selecting previously deselected package linux-headers-2.6.30-020630-generic.
Unpacking linux-headers-2.6.30-020630-generic (from linux-headers-2.6.30-020630-generic_2.6.30-020630_amd64.deb) ...
Selecting previously deselected package linux-image-2.6.30-020630-generic.
Unpacking linux-image-2.6.30-020630-generic (from linux-image-2.6.30-020630-generic_2.6.30-020630_amd64.deb) ...
Done.
Setting up linux-headers-2.6.30-020630 (2.6.30-020630) ...
Setting up linux-headers-2.6.30-020630-generic (2.6.30-020630) ...
Examining /etc/kernel/header_postinst.d.
run-parts: executing /etc/kernel/header_postinst.d/dkms
 * Running DKMS auto installation service for kernel 2.6.30-020630-generic                                                                    
 *  nvidia (180.44)...                                                                                                                        nvidia (180.44): Installing module.
..........(bad exit status: 10)
  Build failed.  Installation skipped.
                                                                                                                                       [fail]
run-parts: executing /etc/kernel/header_postinst.d/nvidia-common

Setting up linux-image-2.6.30-020630-generic (2.6.30-020630) ...
Running depmod.
update-initramfs: Generating /boot/initrd.img-2.6.30-020630-generic
Running postinst hook script /sbin/update-grub.
Searching for GRUB installation directory ... found: /boot/grub
Searching for default file ... found: /boot/grub/default
Testing for an existing GRUB menu.lst file ... found: /boot/grub/menu.lst
Searching for splash image ... none found, skipping ...
Found kernel: /boot/vmlinuz-2.6.30-020630-generic
Found kernel: /boot/vmlinuz-2.6.29-02062904-generic
Found kernel: /boot/vmlinuz-2.6.28-11-generic
Found kernel: /boot/memtest86+.bin
Replacing config file /var/run/grub/menu.lst with new version
Updating /boot/grub/menu.lst ... done

Examining /etc/kernel/postinst.d.
run-parts: executing /etc/kernel/postinst.d/dkms
 * Running DKMS auto installation service for kernel 2.6.30-020630-generic                                                                    
 *  nvidia (180.44)...                                                                                                                        nvidia (180.44): Installing module.
..........(bad exit status: 10)
  Build failed.  Installation skipped.
                                                                                                                                       [fail]
run-parts: executing /etc/kernel/postinst.d/nvidia-common