Problems downloading Twhirl

am having trouble installing Twhirl - it downloads but the file is empty?!
I have tried again and again to download Twhirl. I have listened and re-listened to Ed Dale's 'how to' video on it but it just isn't working! I go thru' the process, but when it installs it does so in the flash of a second and then nothing happens - no account information box, no password request etc. however it is installed on my programs, on my shortcuts, on my screen - but when I click on the symbols to open them there is nothing there.
Please tell me what I am doing wrong!
many thanks,
Sarah