I have a task allocation program that allocates tasks to employees.

The page looks like this:
userid projid TaskID Logon/Logoff
userid projid TaskID Logon/Logoff
userid projid TaskID Logon/Logoff
userid projid TaskID Logon/Logoff

As you can see a user can see all his/her tasks but I want them to log on to a task & all the other tasks logon buttons should be disabled.

How do I disable them??