The easiest way to dual boot with Windows 7 would be ideally to install W7 first, then Ubuntu. This avoids having to reinstall GRUB, which is the bootloader for most Linux distributions.
If you want to install Windows 7 after
Ubuntu, then the easiest way would be to burn a copy of GParted
and allocate a new space. [NOT A NEW PARTITION!]
Once you've got your new empty space, pop in your W7 DVD and then select the new space. Format it, and then install W7.
When you've finished installing W7, you'll need to use a LiveCD or a LiveUSB and boot into the desktop. Typically you'd be better using a Ubuntu LiveUSB/CD.
Open a terminal, and then type the following commands:
To find what the partition Ubuntu is on, is called. e.g. [color="red"]/dev/sdb
You'll what to reinstall GRUB to the MBR, which is where your root
partition is normally installed.
Typically, if your system contains just Ubuntu your root partition would be called /dev/sda1
and your home folder [/dev/sda2[/b]
When you've found out what it's called, you'll need to do the following command:
sudo grub-install /dev/XXX
Where "XXX" is the name of the partition.
Hope this helps ya Matt.