You can use, for example, a 3rd party bootloader like Grub4Dos to install Ubuntu without using external media. Here's a detail description on how to do it. But you will need space on one of you're hard drives to create a partition for the Ubuntu installation. You can not install in you're existing NTFS partition.
An alternative would be to create a virtual machine within your windows an install you're Ubuntu within the virtual machine. You could use for example VirtualBox or VMplayer they are both free. There are "ready to use" installations you can download too, so you don't need to go through the Ubuntu installation process at all.
Here's a short explanation on how to install Ubuntu from ISO using Grub4Dos
title Install Ubuntu
find --set-root /ubuntu-11.04-desktop-i386.iso
map /ubuntu-11.04-desktop-i386.iso (0xff) || map --mem /ubuntu-11.04-desktop-i386.iso (0xff)
kernel /casper/vmlinuz file=/cdrom/preseed/ubuntu.seed noprompt boot=casper only-ubiquity iso-scan/filename=/ubuntu-11.04-desktop-i386.iso quiet splash --
- Reboot and choose Install Ubuntu in the Grub4dos menu.
- After the live desktop loads, open terminal and enter the following command.
sudo umount -l /isodevice
- Now double click on Install Ubuntu.You should be able to install Ubuntu