The image is larger than your screen size. The browser conveniently resized the picture to fit, mutilating the image in the process. In IE, left-click in the lower right corner of the screen and a weird looking "box" icon will appear. Click it and the image will be readable. You can permanently disarm this feature in: Tools -> Internet Options -> Advanced and uncheck "Enable Automatic Image Resizing". In Mozilla or Firefox, just left-click anywhere in the image to toggle between normal and resized images.
There's nothing in the DI-524 router that will limit the number of connections. I also question why this would be necessary. However, it it is required for some reason, you have the problems of how to determine which 3 users are the proper 3 users, how to "expire" any stale connections, and how to handle any secondary authorizations required (login/passwd). These are not DI-524 features, but are commonly found in wireless hot spot software such the various NOCAT based solutions. Some of these require an external computah to do the authorization and user counting. Others can be build into firmware, such as those based on the Linksys WRT54G using HyperWRT or Sveasoft firmware. The scripting capeabilities of the Linux operating system make it possible to impliment a user count limit. Unfortunatly, I don't have a plug-n-play solution for whatever you're doing. If the 3 wireless users are known to you and are not random, then simple MAC address authentication will work.