Problem installing dual boot.

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Hi, I have downloaded Fedora 18 DVD image but I am already running windows so I decided to install as dual boot. when I inserted the DVD in the player. At the time of the partitioning it's taking the whole disk as the installation destination I am unable to partition it into desired space. or I cannot see any free space in that. so stopped installation. Here are my questions

1. Why it's not displaying and not allowing me to redefine partitions on the disk? I wanted to create a new partition in existing free space. which is not fragmented it is continuous free space?
2. Can I install whole fedora in my portable disk?
3. If you have any Guide for the problems I am facing I would be glad if I get it.

Thanks in advance, Sudhir.