For the scenario you've described, you might take a look at SharePoint "Variations", which allows you to push a copy  of content to various sub-sites. Variations are typically used for multi-lingual sites, but they don't have to be used that way. However, I don't know of a good out of the box way of publishing  identical content across site  collections without writing a custom script to do that.

The problem is that Site Columns are defined at the Site collection  level and each Site Column has a unique GUID. Unless a Site Column was created via a Feature, (i.e. it was created in the browser), it will have a unique id associated with it. Even if you created a Site Column in your other Site Collection with the same name, the underlying identifier would be different between Site Collections. That being the case, it would be hard to copy content between Site Collections, because SharePoint wouldn't necessarily know that the content in "My Column" needs to be copied to "My Column" in another Site Collection, if the GUIDs are different.

Luckily, that will be taken care of in SharePoint 2010 with universal content types, but unfortunately, that sort of functionality isn't available in SharePoint 2007.