Windows reinstalling seems to be a very simple and usual thing. As it proved, an unpracticed user can face serious problem while taking to it.
A client came to me with a request to recover Hitachi HDP725050GLA storage vol. 500Gb. Primordially there was only one FAT32 section on the storage, and the user decided to reinstall WinXP, and during installation the storage dic was automatically reformatted as NTFS single section, and OS was installed.
HDD Hitachi GLA
Tables FAT were disturbed greatly. There were many pictures of value for their owner and many works created in Photoshop. Jpeg, and also PSD files that needed recovery as well. Taling into account huge record areas overwritten with new data, I found the only way of files recovery - on the file signature. File hex-name is taken together with its approximate size, special software scans the LBA working area, and as soon as requested headline (signature) is found, file is saved at the server and gets an ordinal name (e.g. file0001.jpeg).
Disadvantage of this method is in the directory structure loss, and also file names and attributes are lost as well, and fragmented files are unreadable. To my great regret, in such a case there is no other way of data recovery.