If you want to ditch Windows completely, Burn the .iso image file on an empty cd-r or dvd-r disk.
BACKUP EVERY PERSONAL FILES YOU WANT TO SAVE FROM YOUR WINDOWS SETUP!!! Burn them on dvd's or put them on USB memory sticks.
Then change your boot sequence from your computer BIOS so that the computer boots from the cd/dvd drive first (you can change this back after you have installed Ubuntu). Usually you can access your computer BIOS by pressing some key when the computer is booting up (like F1 or F8). You will get a simple keyboard-controlled menu with on-screen instructions. Change the boot sequence and exit the BIOS screen.
Pop in your newly burnt Ubuntu live-cd. Now it should boot from the cd. You will get a simple menu from which you can choose different operations (check the dvd for possible defects etc.). One menu item will be "install Ubuntu on your hard drive" or something like that.
Then just follow the on-screen instructions. You already know that your Ubuntu will work on your computer, because it apparently worked no your virtual computer setup, right? The installation process will prompt you for some simple stuff, like your timezone, language preferences etc. You will have to make a user profile (simply give your username - usually your first name - and a password - I'd recommend something you can easily remember, because you will be using it a lot when tweaking your system settings)
When the installation process asks how would you like to partition your hard drive, pay attention. If you choose "use the entire hard drive", Ubuntu WILL WRITE ITSELF OVER YOUR WINDOWS SETUP. After this, if you want your Windows back, you will have to re-install it.
That's pretty much it. You will be taken to your new Ubuntu desktop and you can pop the installation cd/dvd out and stash it for possible future use.
After this, setup your internet connection with the Network Manager (if you did not do it while installing) and upgrade your system through the Synaptic Package Manager (System -> Maintenance/Administration -> Synaptic Package Manager) + install all kinds of neat programs.