The first thing to do is to verify that you did not install the *feature rich* Ubuntu over your windows installation.
Open a terminal and issue this command: sudo fdisk -l.
That will list your hard drive(s) and the partitions on them. Linux partitions (ext2, ext3. ext4, reiserfs are the most common) and windows (ntfs) will be listed. If you do not have an ntfs partition, you have isntalled Ubuntu over it. If the ntfs partition is still listed, then windows is still there and you need to edit the bootloader configuration file to add windows to the boot menu.
You can find instruction for doing that here: http://technologytales.com/2010/11/2...tu-grub2-menu/
PS: Google is your friend. You can probably find answers to most questions abut Ubuntu via google, or at the Ubuntu forums.