Do not use your hard drive with the information until you do this.
If you lose your data (and it is important) buy a second hard drive to install windows on. and then install windows.
Then get a recovery program... I have used EasyRecovery Pro for awhile.
Attach the data hard drive as a second hard drive
scan with easy recovery and have it put desired files on your windows drive.
set up a backup for your data. dropbox is pretty good for that.