System restore deals only with system files.. It doesnt restore for example word files that you have altered.. Atleast.. Not that I know of..
If you overwrote a file there is no way to get it back that I know of either.. Its one thing to delete a file, but overwriting it with another one means certain death.. I've never heard of a way to restore a file that has been trashed like that.
In short.. I think you're out of luck.