Instead of making a myriad of comments, I better write an answer.
I have not used windows8 myself, I can only guess what happened here.
Windows8 uses the so called GPT - GUID Partition Table - to specify which partitions are on the disk. Because this is a totally different concept than the old MBR - Master Boot Record - partition table from the MSDOS era even windows7 still used, the partitions created with either one of these tables are not compatible to the other one.
Well, in theory there should be not much difference between the partitions itself. They are defined by the filesystem they are using (mostly NTFS for Windows). But a new partition table overwrites the old one and thus all information of all earlier partitions will get lost. I have no idea why windows7 only shows a small percentage of your original disk space, it cannot even read the GPT, thus it should show you the whole disk as empty.
Before you do any further damage to that partition, you should try a recovery tool that looks at your drive for abandoned data, or maybe can even restore that partition. I cannot recommend you such tool, because I regularly backup my important files.
Even if it sounds mean, I hope you will learn two things:
Never play around with (beta) operating systems if you have important files on the computer.
And more important: Backup your (important) files.
If you happen to have a backup or were able to restore it, get a partitioning live CD and clean your drive.
As I said above, I never used windows8, everything I wrote is a wild guess. Maybe there is a simple solution to your problem, but I honestly don't think so. It basically costs Microsoft far more money to write a tool that can transfer some wrecked GPT to MBR and vice versa than putting up a warning that all data on the disk gets destroyed. And it is far more likely that you have just not read that warning and just clicked OK... and I wont even hold that against you, everybody does that ;)