Which version you've installed? I think, perhaps, the installation you've done isn't correct, else you would've using it smoothly.
Whenever you install it, it asks for a username and password (which you'll be later using to login the system) as well as gives you an option to partition your system's HD.
Well, if it's not working, then better install Windows again, and then install ubuntu (better go with latest version i.e. 12.04) using USB flash drive.
Hope you know installation process using USB. But if you don't know then simply download the .iso image of Ubuntu from http://www.ubuntu.com/download/desktop
, put it into your USB drive. Insert USB, power on your system, and under boot menu, select USB boot option the first option, and save the changes. Then follow the installation instruction.