How would I go about stitching in MailChimp into a client's site?

I know there's an add-on we can get. But I would rather just do a quick custom ASPX or some customization of aspdnsf objects to make this work.
(I'm still awaiting replies from several other tickets I've submitted to cover exactly HOW to use a custom ASPX page inside aspdnsf. I'm a decent .NET programmer, but documentation is light on the objects/props/events/methods I can access.)

Help please?

Thanks.