I can't seem to download the demo
Were you trying to play it in a browser? That isn't supported, since the rar file (cvd18v2.rar) contains the xovv.exe which needs to be run to extract the game data.
However, if you were just trying to download it normally, I'm not sure what the issue was, since the file appears to be working when tried again that way.
Oh, are you saying you can't open the .rar file once you've downloaded it?
If you're not able to use WinRAR at the moment, here's a version in ZIP.