After you install Ubuntu to a separate partition
on your hard disk, you can definitely uninstall
it completely by following any of the how-to's on
this forum or elsewhere. But if you want an
installation that will be really easy to uninstall,
you could try using wubi,
http://wubi-installer.org/ . It will allow you
to install Ubuntu from right inside Windows, but
still have an Ubuntu system that's essentially the
same as what you would get by installing it to a
separate partition using the Ubuntu CD. wubi
will be a tiny bit slower than a real Ubuntu
installation, but you probably won't notice any
difference. And best of all, if you install Ubuntu
using wubi, Ubuntu can be very easily uninstalled via
the Windows add/remove programs utility. I
would recommend this approach if you want to have the
assurance that Ubuntu can be uninstalled without
a hassle.