Use a hidden HTTP request (AJAX) to fetch files from the same server and have ThickBox display the contents of the files or use an IFrame. In order to open new Ajax content in an open Ajax ThickBox, its code must also contain the appropriate HTML (class=\"thickbox\") to launch an Ajax ThickBox. The only catch is, the ThickBox calls must include both the width and height of the original ThickBox. If you leave it blank the window will resize to the default size(630x440).

public ThickBoxLinkContentModes ContentMode { get; set; }

Public Property ContentMode As ThickBoxLinkContentModes
	Get
	Set