Assigning a Class Name to Attachment Links in Post Body

This may be a question whose answer is obvious to others, but after searching the codebase, I cannot follow the flow of the WordPress code enough to understand the mechanics behind the attachment link insert mechanism.

When I insert a link to an attachment or attachment page in WordPress 2.0, a beautiful ‘rel=”attachment”‘ attribute is added. This works as a style hook for Firefox, but not for IE. I need a hook for IE and am opting for a class name. However, I cannot see a place to modify the behavior of the attachment link.

Can anyone point me in the right direction.