First - fix Windows booting, second - fix GRUB2. Let's start with Windows booting:
Boot from Windows 7 DVD and after choosing language options, start the console:
"Repair your computer" -> "Use recovery tools..." -> "Command prompt".
In the console run the following command to re-install Windows bootloader:
> bootrec /fixmbr
Then rebuild bootsector if it is corrupted, just to be sure:
> bootrec /fixboot
After that You should be able to boot into Windows through the standard Windows booting - no GRUB, no questions - just power on and boot into Windows as in single-boot Windows machine. Now, when Windows boots correctly, it is time to re-install GRUB2:
Boot from Ubuntu Desktop CD and run Terminal. Then mount the / filesystem of
existing Ubuntu installation (/dev/sda2 in this example, but Your case may be different) as well as additional resources:
$ sudo mkdir /mnt/ubuntu
$ sudo mount /dev/sda2 /mnt/ubuntu
$ sudo mount --bind /dev /mnt/ubuntu/dev
$ sudo mount --bind /proc /mnt/ubuntu/proc
$ sudo mount --bind /sys /mnt/ubuntu/sys
After that, chroot to mounted directory and reinstall GRUB2:
$ sudo chroot /mnt/ubuntu
# grub-install /dev/sda
# exit
Reboot and GRUB2 is back. GRUB2 installation should automatically detect all available operating systems and put them into GRUB2 boot menu.