Ubuntu – What version of Ubuntu should I pick?

As others have pointed out, there are many ways to install Ubuntu. The first step is to download the ubuntu-12.04-desktop-i386.iso file, as you have done. Next you have to burn that file into a CD. The instructions are at:

http://www.ubuntu.com/download/help/try-ubuntu-before-you-install

As it says in this page you can try using Ubuntu without installing by booting from the CD you created. This CD can also be used to install Ubuntu INSIDE windows. This method is often called Wubi installation. Ubuntu will reside in a big file in your C: drive. No new partition will be created. Neither will the C: drive be formatted. Once Ubuntu is installed you will have the choice of booting Windows or Ubuntu when you start the computer. To do this kind of install insert the CD while windows is running and follow the instructions. You can read about Wubi here:

https://wiki.ubuntu.com/WubiGuide/

Hope this helps.

Method 1 - If you just want to create a user with a given UID

1. Install Ubuntu normally
2. Log into Ubuntu
3. Open a Terminal
4. Create a new user with the ID 1200 sudo adduser -u 1200 <username>
5. Confirm that the user was created with the desired id awk -F: '/\/home/ {printf "%s:%s\n",$1,$3}' /etc/passwd
6. Add the newly created user to the sudoers group sudo adduser <username> sudo
7. Logout
8. Login with the newly created user
9. (optional) Delete the old user

Method 2 - Automated Ubuntu installation using preseeding

In order to be able to define a UID range at installation time, you need to automate the Ubuntu installation using preseeding, which is basically

a way to to set answers to questions asked during the installation process, without having to manually enter the answers while the installation is running. This makes it possible to fully automate most types of installation and even offers some features not available during normal installations.

Using this method, which is way to extensive to be posted as part of this post, you can (amongst many other things) setup the account which will created at installation time. Example:

# Skip creation of a root account (normal user account will be able to
# use sudo). The default is false; preseed this to true if you want to set
# a root password.
#d-i passwd/root-login boolean false
# Alternatively, to skip creation of a normal user account.
#d-i passwd/make-user boolean false

# Root password, either in clear text
#d-i passwd/root-password password r00tme
#d-i passwd/root-password-again password r00tme
# or encrypted using an MD5 hash.
#d-i passwd/root-password-crypted password [MD5 hash]

# To create a normal user account.
#d-i passwd/user-fullname string Ubuntu User
#d-i passwd/username string ubuntu
# Normal user's password, either in clear text
#d-i passwd/user-password password insecure
#d-i passwd/user-password-again password insecure
# or encrypted using an MD5 hash.
#d-i passwd/user-password-crypted password [MD5 hash]
# Create the first user with the specified UID instead of the default.
#d-i passwd/user-uid string 1010
# The installer will warn about weak passwords. If you are sure you know
# what you're doing and want to override it, uncomment this.
#d-i user-setup/allow-password-weak boolean true

# The user account will be added to some standard initial groups. To
# override that, use this.
#d-i passwd/user-default-groups string audio cdrom video

# Set to true if you want to encrypt the first user's home directory.
d-i user-setup/encrypt-home boolean false

Notice the line:

# Create the first user with the specified UID instead of the default.
d-i passwd/user-uid string 1010

If you want to learn more about automated installations there are several sources of useful information in the Internet. This is the official documentation currently:

https://help.ubuntu.com/lts/installation-guide/armhf/apbs01.html