If you want to reinstall ubuntu only to change the partition size, you don't need to do that. You can use GParted (System - Administration) to resize the partitions, reducing Windows D partition and increasing Ubuntu's partition without reinstalling.
To install gparted:
sudo apt-get install gparted
If you need to reinstall for another reason, you can also use gparted to resize the partitions before reinstalling ubuntu with the live CD. I think it is safer than to do it with the installation program as you can control better what you are doing.
EDIT after question edit:
I think you can get the same result with the installer and with gparted alone but I feel you have more options and control using gparted before than within the installer.