Adding options to the User CP

[gdguide]

On our forum we have a set of rotating header images, but the PHP that is used to rotate them doesn't perform well on old versions of IE. I'd like to add a single checkbox in the UserCP that enables a "optimize for IE" setting, and wrap the IE-specific header code in an <if>...<else> tag that would check for the status of that option for each individual user and display the header accordingly. How would I do this?