This website should allow users to enter their usernames on various chat programs (AIM, Yahoo Messenger, MSN, etc).
It should also allow them to enter a comma-separated list of topics they'd like to chat about.
Then it should list them in the database of people who want to chat about that topic. The front page should show the 100 most popular topics, and should also be searchable.
Clicking an icon for a chat service should pop up whatever program is used to use that service.
Entries should expire in one hour. I have attached a file which gives a basic outline of the site.