First thing to do is to start thinking in GNU/Linux terminology. There are no C or D drive; they are devices listed in /dev. The first drive is /dev/sda, the second is /dev/sdb, and so on.
So, you have Windows installed on /dev/sda. If /dev/sda is all one partition, then windows is installed in /dev/sda1 (the 1 means the first partition on drive /dev/sda).
You want to install Ubuntu on /dev/sdb. When the installation is complete you will have two partion on /dev/sdb: /dev/sdb1 (the root of the filesystem) and /dev/sdb2 (swap).
During the installation process, you will have the opportunity to select the drive for installation. Be VERY CAREFUL to select /dev/sdb for installation of Ubuntu. You should also have the opportunity to select a volume of space on /dev/sdb for the swap partition.
If you want Ubuntu's bootloader (grub) to boot either windows or Ubuntu, the installation will write the first stage of grub into the MBR of /dev/sda, and it will write a configuration file which will show you a menu on boot that allows you to select which OS to boot.
Note: Make a copy of your MBR on /dev/sda (before installing Ubuntu or any other GNU/Linux distro) and save it somewhere (in your windows Documents should suffice). In future, if you want to get rid of Linux on /dev/sdb, you will have to either restore that copy of the MBR, or use a windows install disk to run fixmbr. Just a word of advice.
Search these boards for info on how to use the dd command from a liveCD to make that copy of your MBR.
PS: most if not all problems you encounter have already been answered. Use www.google.com/linux
to search for answers to questions you might have. If you can't find the answer, then post your question here. Linux is a learning process as much as it is an operation system. The link above will help you in your learning experience.