Installing UBUNTU on MAC using Parallels Desktop

To install any Linux guest OS on Parallels Desktop, we need to download the respective .dmg from http://www.parallels.com/ptn/download/va/?categ=5&sort=rating&lsort=www

Now at this time, the latest release of UBUNTU for Parallels is 8.04.1 and is available at http://www.parallels.com/ptn/download/va/?va_id=228 Click getApp and download the .dmg.

Administration Interfaces:

GUI
Login: ubuntu
Password: 123

I tried downloading .iso files directly from ubuntu site but could not set it up as it asks for a partition !
Also no luck downloading the CentOS.iso from its site, it wouldn't even create the VM.
Windows 7 gets installed fine !