Can I have more than one WUBI installation?

Please tell do you want to simply have Ubuntu and Kubuntu... on the same pc ?
If yes, you don't need to install Ubuntu twice...

Please simply install the meta package kubuntu-desktop and or kubuntu-kde4-desktop on the already installed Ubuntu and then you will able to choose the Desktop Manager you want to start a session before login...

So please simply open a Terminal from the menu Applications → Accessories → Terminal and type:

sudo apt-get update

sudo apt-get install kubuntu-kde4-desktop
or
sudo apt-get install kubuntu-desktop

give your user password when requested, you don't see nothing when you type it, then press enter.

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As new user i want suggest to you my best solution:

1) - Strongly i do NOT suggest you to install Ubuntu using Wubi. Wubi is Windos Ubuntu Installer.
If you install Ubuntu using Wubi, when a virus or other issue coming into Windows them will affect your Ubuntu too...
Please make a real and separated from Windows Ubuntu ext3 partition on your pc.
To install Ubuntu NOT using Wubi please simply boot your pc entirely from the Ubuntu live install cd... don't run installer using Windows.
You must not see Windows starting when you are about to install Ubuntu using the Ubuntu live cd.

2) - Please install Ubuntu 8.04.1 standard 32 bits:
- it run fine on 32 and 64 bits pc
- it is a LTS (Long Time Support) release, supported for 2 years, and when you will see the Ubuntu 8.10 solved you will easily upgrade your release... from Ubuntu 8.04.1 to Ubuntu 8.10

Hope this helps

Or better install the Ubuntu 8.10 http://releases.ubuntu.com/8.10/

Hope this helps

The computer I am using is a work PC, so I can't install ubuntu natively. I already have one WUBI installation, and I want to install another for experimentation purposes.

Thanks, I'll go ask on the WUBI Q&A.