SharePoint Designer - how to edit a page?

In SharePoint 2003 (WSSv2) with FrontPage, it was so easy to edit a page. Just open the page you want to edit in Internet Explorer and hit the "Edit in FrontPage" icon at the toolbar.
Well, the good news are that in SharePoint 2007 (WSSv3) the same applies, but only for some of the pages, while other pages will tell you "This page cannot be edited in SharePoint Designer".
This article will explain what is going on, and how to get each type of page to be editable in SharePoint Designer.
Lets start easy- when you create a WSSv3 web site from one of the default template such as team site, blank site etc...you will have no problems using the easy button -edit in SharePoint Designer.You can also open the SharePoint site or page for editing from within SharePoint Designer using the "Open Site" or "Open.." dialogs within the application.
When you open such a page from such a site directly from Internet Explorer, or from SharePoint Designer, you will see the page in SharePoint Designer, and be able to modify it using the designer mode or the code mode.
So far so good right?
So lets figure out why some of the pages give us the following message when we try to edit them in SharePoint Designer:
"This page cannot be edited in SharePoint Designer. You can edit the content in the browser, or edit the corresponding page layout in SharePoint Designer"
Why is that? well, simply because the page you are trying to edit is under the publishing feature. It is a publishing page, and as such, by default, gets it's layout from the layout page and the master page.
The only change you should be doing on such a page is edit it in the browser and add\remove\change web parts in it.
However, there is a way to work around this - detach it from it's layout page. This is similar to the ghosting\unghosting process that we had back in SharePoint 2003 (WSSv2), but with the added benefit that we can allways roll back the change.
It also means that in the first time you will edit that page, you will have to start from SharePoint Designer to do it:
Open the site that contains the page in SharePoint Designer (use "File>Open Site") and browse to the page you want to edit in the folder list.
Right click the file, and choose "Detach from page layout". This will unghost the file - copying it's layout from the layout page into the database, and so allowing you to edit it, just like you used to do in SharePoint 2003
Unlike sharepoint 2003, you can take it back, and reattach the file.