Creating custom forms to map to content types

I'm looking to create custom form pages, which then map the fields on the form to a particular content type (I'm using CCK but I don't see why it needs be limited to that), with default values for the content type's fields which aren't visible on the form (although ideally this would only be needed for mandatory fields in the content type).

Ok, so this is what I'm looking to do. I've created a "cost-logger" content type, with fields including "Item name", "cost", "date", "catagory" (taxonomy type), "note". And I want to have a form which doesn't display all the usual node creation form stuff. That is I want ONLY a very simple clean form, which I can then use in a block entry form. Kind of like the shout-box module - in fact one would probably be able to do that module if I can do what I want to do, the only difference would be that each entry would be a node.

Any ideas how to do this with pre-existing stuff? Or if not, would the best way to go about it to create a module for creating custom forms that then somehow does the mapping? (any ideas on how to go about doing this?)

Cheers

Daz