I have installed Ubuntu 12.04/ 32-bit using Wubi on my laptop running dual with windows 7 desktop and it works very very well. I am now also trying to install Ubuntu on another laptop already running a linux operating system only but not successful in doing so. Would like to install Windows 7 dual with Ubuntu. At the moment it is complaining about partitions of the existing linux when trying to install Windows 7 which I suppose is fair. Please herewith assist in installing the Ubuntu and Windows 7 platforms. Very much appreciated.
Did your Linux installation take all the HDD space on your notebook? If the answer is yes, then you probably can't install Windows 7 over Linux/dual boot. If there are more space, you probably have to prepare another partition for installing Windows 7 using Gparted (in Linux).
And beware, if you install Linux first then Windows 7 after it, you probably face another booting problem, which will required you to fix your grub/lilo.