I was under the impression that Windows 7 Home Premium was about 10gb in size. If that is true then why is it taking up 20 gb of my hd space. I have a 40gb drive with nothing but my os on it and i have 17 gb left. Why is that?
Windows restore points would account for the extra space used. They are created after each Windows update.
They can be switched off by going to the control panel, System and Security and click on System, then System Properties and System restore.
If you turn them off you won't be able to restore until you enable it again, but you will only have the new restore points from the time you enable it, all previous points will be lost.
This is not all bad news, if you are not having any problems, the new restore point will get you out of trouble if an update later creates a problem, you can restore the latest one created.