The windows installer is not likely to detect the Ubuntu install, and will overwrite the entire drive by default unfortunately. There are ways to create separate partitions with Gparted\windows tools to create an additional install partition, but that can be a bit tricky.
In my experience, the Ubuntu installer does a good job of detecting Windows installs, and will do all the difficult partition resizing for you -- I have 3 computers dual booting Ubuntu\Mint\WinXP\Win7\Win8(non-uefi)
Steps for a simple clean dual boot(Ubuntu 13.10):
- Backup all important files
- Install Windows, and allow it to format entire drive(make sure install is 100% complete)
- Boot into an Ubuntu live session(CD or USB)
- Use the installer from the desktop
- The installer should offer an option to install alongside Windows 7
- Select how much space each OS gets and wait for it to finish.
- Your computer will now boot into GRUB and allow you to select Windows or Ubuntu each time you boot.
It's unfortunate that this did not work for you the first time, but I know it should work, barring any encryption\odd partitions.
To help you get Windows iso on a bootable USB: http://www.microsoftstore.com/store/msusa/html/pbPage.Help_Win7_usbdvd_dwnTool
Linux Mint(based on Ubuntu) also has an ISO to USB tool built in, and it may be installable in Ubuntu as well:http://community.linuxmint.com/software/view/usb-creator