Installing ubuntu partitions problem

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http://askubuntu.com – I'm an Ubuntu newbie and I'm using it for the first time. During the installation I chose install Ubuntu over Windows, thinking that this will keep the partitions and install Ubuntu on the partition where the Windows was installed (C:) and keep the other one (D:) with all the files on it. After I installed I couldn't find the D:\ partition. Was It formatted as well, and if yes is there some way to retrieve it? Please help I'm desperate, I had some really important files on that partition! (HowTos)