How to Display List of TextBoxes Similar to Group On ASP .NET Page

I have a list of entries that a user needs to check if they are signing up for on a web page, similar to a list of checkboxes, but the last one allows for a manual entry for an "Other" category that will be processed by the site. How do I get all of the checkboxes to limit there to only be one selected, without setting up a complex condition that checks to make sure that only one of the checkboxes are displayed? How do I display the list of check boxes in a structure similar to a group of checkboxes, that would normally be a checkbox list except for the limitation of the manual entry of the last category? (Would a panel be the best way to group these? Would it add any benefit to organizing the web form?) Any help would be greatly appreciated.