There's not much to go on here but it sounds like you are looking for the Admin Skin functionality. The admin skin is the skin used when you are editing the contents of a module.You can specify the Admin skin in Site Settings. There are definitely cases, and I suspect this is one of them, where it's helpful to have a separate Admin skin.
But generally, I'm not aware of any cases where DotNetNuke will prevent you from doing something you can do outside of DNN. There really are no limitations in it's skinning implementation, as it exposes the full capabilities of ASP.NET. The only caveat is sometimes some additional unwanted markup is added around your content. With DNN6, they are making the rendering of lots of elements cleaner and more semantic.