Coding is your friend - Interface Builder will be of no use here.
Probably best to subclass UITableViewCell and add a button as a subview during cell initialisation, but you don't have to subclass.
If you don't want to subclass, you can initialise the button somewhere within the cellForRowAtIndexPath method (I normally create the tableView:dequeueCellWithIdentifier: and configureCell:atIndexPath: methods as in some of the Apple examples). The key thing is to add the button as a subview of the cell's content view in a similar way to how you would add a custom label:
Code:
[cell.contentView addSubview:myButton]
There are several good examples that illustrate this (e.g. UITableView examples 1-5 or perhaps CustomCell).
Don't forget to release your button instance once you have added it as a subview as the parent view (in this case the cell's content view) retains its subviews at the point you add them.
Hope that gives you a starting point.