I have not used a Linux distro before, but want to give Ubuntu a try. I have some knowledge about WUBI. Do I need WUBI to install Ubuntu 14.04 with Windows System 7?
From my own experience Wubi installer for Windows works best with Ubuntu 12.04 LTS and some of the other operating systems which are part of the Ubuntu family like Xubuntu 12.04 LTS or Lubuntu 12.04 LTS.
If you're planning to test Ubuntu first in a dual-boot configuration with Windows, then wubi installer is a good way to start but you will be limited to only 30GB of space when installing Ubuntu. Other than that, Ubuntu will boot fast, and you will be able to use Ubuntu in a very similar manner like when installing Ubuntu on a separate Linux partition.
If you want to play it safe, and don't have plans for the moment to change your partition table adding the necessary Linux partitions for installing Ubuntu, wubi installer is the right choice. Once you get used with this new OS, you can decide later on to install Ubuntu 14.04 inside a real Linux partition.
It is recommended to download and install the same architecture for Ubuntu like you used it when installing Windows. If you have Win7 64bit, you should download and install Ubuntu desktop 64bit iso image for the wubi installer. If Win7 is a 32bit version, choose Ubuntu desktop 32bit iso image from the list of available iso images for Ubuntu 12.04.
To be able to install Ubuntu 12.04 easier using wubi.exe, you should first download both wubi installer and your preferred Ubuntu iso image, place both files in a temporary folder on your desktop, and start wubi installer from inside that temporary folder. After reboot, allow the installer to finish installing Ubuntu, and only after a second reboot you can choose Ubuntu from the boot menu list and hopefully boot into your newly installed Ubuntu 12.04 LTS.
Read this Wubi Guide, it may prove useful for you.
If you just want to try out Ubuntu instead of installing it for good, I recommend virtualization. Go to http://www.virtualbox.org and download Oracle VM VirtualBox in Windows. Then, you can install Ubuntu in a virtual machine, meaning that the entire operating system runs in a window as a program, and uses a "virtual" hard drive that is actually an ordinary file. For more information on virtualization, go to http://en.wikipedia.org/wiki/Virtualization.