There are several ways for Web Parts to show up in the Add Web Part
dialog:
1. A List was created in the site where the Web Part is being added
Scope: Site in which the list was created

2. A .DWP or .WEBPART file  was imported (manually or using a Module
Feature) into the Web Part Gallery in the root site of the Site
Collection
Scope: All sites in the Site Collection where the Web Part was imported

3. A .DWP or .WEBPART file was copied to the file system wpcatalog of a
Web Application (manually or using a WSP CAB) on every Web Front End
(WFE) in the farm
Scope: All sites in all the Site Collections in the Web Application
where the Web Part was copied

It is also possible to import the .DWP or .WEBPART file from the file
system directly onto a page  (not from a gallery). Of course, the related
assembly must already be deployed to all WFEs. Also, if a Web Part was
previously on a page and subsequently closed, you will find it in the
Closed Web Part gallery in the Advanced Tool Pane (same as the v2 Web
Part Gallery Tool Pane).

So, the Add Web Part dialog presents an aggregation of Web Parts for all
site Lists plus all the Web Parts in the Site Collection's Web Parts
Gallery, plus all the Web Parts in the wpcatalog for the Web
Application.

It does..with one exception..
It's the descriptor for the web  part PAGES that I need..like when you go to
create>new web part  page and you see the 8 choices..(header, three column, full
page, etc..)

those are a throwback to before v2 when they were called Smart
Pages. You can find those eight pages  here:
...\12\TEMPLATE\1033\STS\DOCTEMP\SMARTPGS\spstdN.aspx

You can choose to show less but you cannot have any more than eight
pages, period. They remain there for backward compatibility and I
wouldn't hold my breath for the likelihood that they will be there in
vNext (I haven't heard one way or the other so I'm just speculating).
The new approach is to use MOSS Publishing with content pages created
from page  Layouts and stored in the Pages library.

Instead of adding, I want to change one of the existing spstd pages..which I
have done..but I need to change the descriptor that shows for my custom page..