GRUB install fails

I am trying to install Zorin OS 5.1 in a HP dv6 series laptop which has preinstalled Windows 7 in it. I have made changes to hard drive and have 4 partitions for Linux (all logical partitions):

/dev/sda6 /boot ext2
/dev/sda7 swap
/dev/sda8 / ext4
/dev/sda9 /home btrfs

I successfully installed Ubuntu 11.04 32-bit in the above partitions and was working fine. I decided to install Zorin 5.1 instead and since it is based on Ubuntu 11.04, it should have worked, but GRUB installation fails with a fatal error. Since I cannot install GRUB, I chose not installing it and continue with installation, but right at that point the installer crashes and the only thing I can do is to restart the laptop.
The on-screen message asks to file a new bug at "https://launchpad.net/ubuntu/+source/ubiquity/+filebug" which I have done.

The bootloader for the laptop is Win 7 bootloader and I had added entry for Ubuntu 11.04 and was working fine. In order to use Win 7 bootloader, GRUB must be installed in the "/boot" (/dev/sda6) partition, NOT in MBR. The laptop did not come with a Win 7 install disk, so I do not want to mess with MBR at the moment.

Any suggestion for this issue?
Thank you!

root and home should be ext4 and if you already have Win7 on the PC, you don't need a boot partition as the installer will automatically select the MBR for you!!.

Regards Wolfman

With respect to the above replies, I have done the emergency and restore disks generation before I resized the partitions and installed Ubuntu 11.04.
As I wrote in my initial post, the following partitions works fine for Ubuntu 11.04. Also root and home do not have to be ext4 partitions.

/dev/sda6 /boot ext2
/dev/sda7 swap
/dev/sda8 / ext4
/dev/sda9 /home btrfs

GRUB bootloader installed in "/boot" (/dev/sda6) partition, NOT in MBR.

After installing Ubuntu 11.04, since MBR has not been modified by GRUB, PC boots ONLY into Win 7. You need to download and install "EasyBCD" (http://neosmart.net/blog/2010/welcome-to-easybcd-2/) and add an entry to Win 7 bootloader.

I decided to install Zorin in the above partition arrangement (I selected to reformat them during Zorin install). I think the problem is the Zorin install script which wants to install in MBR only. When GRUB install fails it opens a window and give me an option not to install the GRUB and warns that the system will not be able to boot into Zorin and I selected that option also so I can complete the installation but that also fails. I can manually install the GRUB if the installation finishes, but I do not get that far.

Thank you for your replies and I hope one of the Zorin developers look at my issue and suggest a solution.

You can try this guide with the Ubuntu 11.04 Live CD: http://maketecheasier.com/restore-grub- ... 2010/05/05