I am using Internet Explorer 9 and when downloading a large file I clicked "open" but then my computer got restarted (presumably after the download finished). Can I retrieve the download? I'm not sure where the temporary download folder is for IE but maybe it's there.
You should be able to get to it pretty easily.
In IE press Ctrl+J to open the download manager, click "Options" -> "Browse", then just check where these files are being downloaded. Since it's a recent file you should see it in the window. This way you will not only get your download, but you will know where your downloads are.
If your download is finished you should be able to access your file, if not then you should be able to restart it.