Multiple questions for you. :-D
1. Do you want to dual-boot? (i.e. run Windows and Linux at on the same drive, and choose which to use on startup)
2. What are the stats of your computer (reason for this is: is ubuntu ultimate the right choice for you?)
3. Are you sure you want to use Ubuntu Ultimate? (It is Ubuntu with every damn package imaginable installed on it.)
If you only want to run Linux, the installation will give you the option of using the whole drive, this will erase Windows for you.
If you want to dual-boot, you use GParted
and make your NTFS partition smaller and install your Linux distro on what is left.
Hope that helps ;-)