Stephen:
It depends what you're looking to do!
Using Javascript is pretty difficult to work into the Marketo editor, as are some fluid width designs. It's definitely possible, but requires some more technical knowledge.
Having someone design a landing page in a separate program like Photoshop, recreating that is definitely possible with Marketo. It takes some creative thinking, chopping up the images so that they'll work with Marketo's landing page editor, but it's very possible. We prefer to have an actual designer come up with the aesthetics, then someone with more technical skills can turn the design into a native Marketo landing page.
Best,
Edward Unthank