Hey,
You can only install dapps on other nodes if the owner of the node wants this. If they don't want that, they protect it by setting up a master password. I will ask Oliver to install the Guestbook again, so you can try it out.
The other ones are most probably by community users and they are most certainly not working.
The long-term solution will be that you are running the full client and install the dapp locally on your computer. Another option is that you will be running a lite client which will make it possible to connect to other nodes which already have the dapp installed, and use them.