If you like Windows user interface or you are confused with ubuntu user interface you can easily convert it to Windows XP or 7 GUI. You can easily uninstall theme when you want and everything will be like it was before theme is installed. Also installation of theme is for one user so if you log in other user it will remain it old theme.
Ubuntu linux when installed Windows 7 theme:
If you want to install Windows 7 theme follow steps on this link: http://deviceguru.com/making-ubuntu-look-like-windows-7/
Ubuntu linux when installed Windows XP theme:
If you want to install Windows XP theme on Ubuntu linux do this:
Just download the tar.gz file, Right-click it and select "Extract Here", then run the "InstallXpGnome.sh" by double-clicking it and choosing "Run"!
More about Windows XP theme on this link:http://ubuntu.online02.com/node/14