I have an old Dell Inspiron 1525, which was only having ubuntu 13.04 installed previously. For reasons not relevant to this post, I had to install Windows Vista that originally came with this laptop. For installing Windows, I moved the Ubuntu installation to a logical partition. Before installating Windows, I had verified booting Ubuntu 13.04 from the new partition. But after installing Windows Vista, the Ubuntu partition is showing as unallocated. I have other partitions (all ext4) and they are all intact. I have checked the partition layout with gparted and also Windows disk managements. Its only the Ubuntu partition that is showing unallocated/free.
Is it possible to recover this Ubuntu partition? And if yes, what are the steps?
It sounds to me like you told the installation of Windows to use the entire hard drive and it simply deleted all partitions and created new one(s). Recovering a partition is usually a difficult task but it gets more difficult and even impossible if you have overwritten sectors with new data. See here. If you have Windows there are other tools that you can use (->Google). Hiren's Boot CD also has a collection of recovery tools. Don't forget: try to avoid writing data to the hard disk as much as possible. Best way to do that is to use bootable OSs (Ubuntu Live, Hiren's Boot CD etc) because such systems load directly into the memory and do not require writing data to the HDD unless being told to do so.