Although you can save a step by setting up windows on only part of your
hard drive from the start, most people don't have trouble resizing the
hard drive with windows already installed on the complete hard drive. I
have done so on over a hundred PCs using gparted. Gparted is on the live
disk and what is used by the installer when installing Ubuntu. You can
use Gparted by selecting try Ubuntu when the computer starts from the
disk. I have found that some newer machines are setup with all four (
the limit) partitions. I always make an extended partition to install
Ubuntu on no matter how many partitions there are remembering that if
there are 4 you must remove one to continue. The installer will start
with to many partitions being used on the hard drive but will fail.

If the set up fails to complete the grub is not installed. said another
way, the setup program waits until it feels the setup went without a
snag to install the grub because installing the grub with a broken
system is a make or break proposition. well it is if you don't know what
you are doing anyhow.

What can make a setup fail?

A piece of hardware that drivers are not available for. This problem is
more pronounced with no Internet connection.
Some machines I have installed Ubuntu on, had Wifi cards that drivers
had to be downloaded for. The install completed but the Wifi did not
work until the drivers were installed. I had to use a 3G or Ethernet
connection to complete the install. I find it easer to install from the
gitgo with an Internet connection rather than with WiFi.

When an important piece of hardware is not recognised, the install can
take a very long time. this is because it keeps looking for a substitute
driver or whatever. It is likely the install will fail, even if you let
it take it's time. You can complete the install by going into BIOS and
turning off offending hardware. I had to do that with the first install
I attempted, this was before athros wifi cards were supported.

When all is said and done. The only recent failures I have had, were
when all 4 partitions were taken by the manufacturer (an easy fix
because the tools partition tools can be downloaded from the
manufactures site). Also one time with a faulty piece of hardware (fully
supported). The time that comes to mind, the boot sector was failing and
the owner wanted to install Ubuntu to try to fix the machine that
wouldn't work with the Windows that was already having problems on the
machine. A new HD and off he went.