Solution 1:

Yes, if you have both wubi.exe and the ISO image for the same release, you can make Wubi use the ISO so it doesn't have to download the files again. This makes installation considerably faster!

  1. It's advisable to check the MD5SUM on the ISO image, to make sure it's good.

  2. Put the ISO image and wubi.exe in an empty folder.

    Technically there could be other files in here, but it would be confusing, and once you get additional Ubuntu ISO's in there, which sometimes happens for users who are trying different versions, it would be a bad situation.

  3. Run wubi.exe to install Wubi.

Screenshot showing ISO image and wubi.exe in the same folder, with wubi.exe about to be run.

That's it. With the ISO image in the same folder as wubi.exe, the Wubi installer will automatically attempt to use the ISO image (and assuming it's an ISO for the same version of Ubuntu, and the ISO is not damaged, there should be no problems).

Assuming everything goes well, it should be possible to install without even being connected to the Internet when wubi.exe is run. However, if possible, it's recommended to be connected to the Internet while installing Ubuntu (whether you install it inside Windows with Wubi as you plan to do, or alongside/replacing your existing Windows or other OS by by booting a CD/DVD?USB).

Remember, the Windows installer (wubi.exe) and the ISO image should be for the same release of Ubuntu.

Solution 2:

Windows 8 currently uses UEFI so it might be problematic with Wubi on Windows 8 so you have to download Rufus (fastest one that I have tested) and the ISO.

Download Rufus: http://rufus.akeo.ie

Since you have already the ISO File plug your USB Device in a fastest port possible to ensure that Rufus will install system files in a faster way.

After plugging in, Follow these steps:

How to make Ubuntu USB:

  1. Download Rufus above
  2. Plug your USB Device before running Rufus
  3. Click on the CD icon on a button so Select the ISO dialog is displayed
  4. Navigate to Ubuntu 14.04 LTS ISO File
  5. Click START
  6. Wait for a few minutes. It should complete it successfully.

Ensure that your BIOS supports USB Booting so you can run Ubuntu from there, If it does not support USB booting (like my computer), then you will have to download and install another boot manager (plop boot manager) so you can boot from USB.

How to boot from USB Drive:

  1. Restart your computer
  2. Put the key where it leads you to the BIOS Boot Menu, It should have the option like (USB HDD: )
  3. Go to the USB HDD or something similar and press enter
  4. It should boot, After booting, Press the Install Ubuntu

How to install Ubuntu:

  1. Follow the installation steps until you have reached with Install Ubuntu alongside Windows 8
  2. Click the Install Ubuntu alongside Windows 8 button
  3. Follow these 3 steps and when you are finished, you should have the slideshow with the progress bar.

How to finalize installation:

  1. After installation is complete, Restart your computer
  2. Unplug your USB Drive after your computer/laptop actually boots into BIOS to avoid restarting the installation depending on the boot order
  3. Select Ubuntu when you are presented with Windows, Ubuntu.
  4. It should boot.