You can try out API calls here. This will allow you to troubleshoot signature generation and see the actual xml result of your calls. Your api secret is never transmitted over the internet, so it should be pretty safe.

Instructions:

1. Enter the API key and secret that you want to test.
2. Select a method (vimeo.videos.comments.getList)
3. Add the required parameters (video_id = 375747)
4. Click "TEST"