I've created a drupal views Attachment display that lists a bunch of nodes. How would I add this to a content type? I've seen examples that require changing the template files, but can views Attachments be used without making changes to the theming layer?
Views attachment displays attach the display to another display within the same view: look at the Attachment settings block on the attachment display. The use case for this is if you had, say, a summary view and a detail view that had to appear together: you'd attach the detail view display to the summary view display.
If you want a view to show up on pages other than the view itself, you need to create a block display. Then, you have two choices:
If you want it to show up in a region defined by your theme (i.e. as a regular block), just go to Site Building -> Blocks and move the newly created block to whatever region you want.
If you want it to show up as part of a node, you need View Reference, which creates a CCK field that lets you select a view. That field can be positioned anywhere in your node template like any other CCK field.