You can use UNetbootin to install Ubuntu 15.04 from Windows 7 into a dual boot system without the use of a cd/dvd or a USB drive. I am writing this from a fresh Ubuntu 15.04 install using the method below.
Backup all your files...just in case
Defrag your C:\ drive [right click C drive>click on Tools Tab>Defrag]
Check for errors [right click C drive>click on Tools Tab>Error Checking]
reboot and wait for the app to finish completely, the system will reboot when finished
Create Unallocated Unformatted free space on the C drive
[Control Panel> Administrative Tools>Computer Management>Disk Manager>right click the C drive>Shrink Volume]
I believe the suggested space for a full Ubuntu install is 16 Gig, I made 41,000 MB about 40 Gig. Just type the size into the already selected box. The wording MS uses is confusing be assured typing 41000 will make 40Gig free space. click next if it asks to format DON'T Also Do Not assign a letter to the newly made volume.
Reboot Windows 7 a couple times to be sure the changes in the volume have taken without errors
Download the Ubuntu 15.04 ISO
Run UNetbootin [choose disk image radio button and select the Ubuntu ISO image you downloaded. Make sure that Type: Hard Disk is selected in the drop down. Make sure Drive: C:\ drive is selected in the drop down. Click OK] The program will run through 4 steps and then ask to reboot now...Comply
During reboot you will have a choice between Windows and UNetbootin, [Choose UNetbootin] This will boot a Live CD try before you install desktop.
After you look around a bit you will notice an Install Ubuntu 15.04 shortcut on the desktop [start the install, I think the 4th step of the install shows the main volume with Windows and the free space you created using Disk Manager. [Make sure you click the free space and set it for "/", click continue install] Takes a few minutes then it will reboot automatically. If you don't press any keys it will default to the Ubuntu OS. Let it boot. setup your WiFi look around a bit then reboot when you are ready. Upon reboot arrow to Windows and it will boot Windows 7 boot loader where you will see the UNetbootin is still a choice. Windows will be the default there and allow to boot.
As I stated before I am typing this from Chromium running on Ubuntu 15.04. I wrote all this so you wouldn't be worried about using other partition software such as Gparted or Parted Magic. No need to purchase anything Windows already has a good tool> Disk Manager
I'll be honest I still need to figure how to uninstall the UNetbootin loader from the Windows boot loader but that is a small issue, I just "Frugal Installed" Ubuntu successfully. :)