Fail to install fedora domU

I just had installed Fedora 7 with virtualization package using installation DVD. I run the virtual manager and try to install a para-virtualize fedora domU. I had followed all the steps which i found in 
http://www.howtoforge.com/xen_gui_fedora_7_desktop but still it shows that a message that says failed to locate the disk image.

I even had 'yum install vnc' and yet the same error still occurs.
Do i need to manually create a 
disk.img file before setting up a domU?
Need help on this...

Neohtm