Why don't you dual boot using wubi instead of giving ubuntu partion(s) of its own? You wanna get rid of it? Go to your application list in the Windows Control Panel and uninstall it just like you wuold do with any other Windows application. It takes 15mins to install ubuntu and 5secs to uninstall it. AFAIK only drawbacks for ubuntu are: no hibernation available, slower disk access (ubuntu FS is actually a windows file). Apart from these, you wouldn't tell it apart from a native clean installation.