Just out of curiosity: why are you using Fedora 15? Is that the exact version your college is using or something? Fedora 15 is no longer supported, I would recommend you grab a newer version instead (unless you have a reason stay with 15, of course).
Anyway, on the actual problem: can you see your Windows partitions from Linux (just go to the file manager and see if any large-ish volumes appear that you know aren't external HDs or anything of the sort). If not, you've probably overwritten your Windows installation... which option did you choose when the installer asked about hard drive partitioning? I think the default is to wipe everything and let Fedora have the entire disc, if you went with that... everything you had on Windows is most likely gone and irrecoverable. If you see the windows partition, though, the above should do the trick (though why didn't the installer do that automatically escapes me).