The first two can be accomplished OOTB with Windows SharePoint Servics
(WSS). The third feature is available OOTB with SharePoint Portal Server
(SPS) but not WSS however there are some 3rd party tools that enhance
WSS search  capabilities that I *think* will allow you to do metadata
searches.

But still I can't figure out the
configuration and where is it to be made. Can you please provide me some
pointers on how to configure WSS (or SPS) to use these Meta tags  to
upload documents? Are these settings made at document  library level or
Site level? I was unable to find anything in the WSS or SPS admin  guide.
Looking forward for the response.

i saw your mails.firstly u have to explore the options in SPS
yourself.because there is very less in the help files or guides.Now for making
these new Meta Data fields in the document  library log in as SPS admin.first
create a document library if you have not already done so.If it is already
created open that document library.In that document library on the left side(in
quick launch) there is a link "Modify settings and Columns".Click on that link a
new page will open here under the heading Columns there is link "ADD a new
Column" click on that link a new page will open at this page you can give the
relevant details of that column(field) including its data type and values
etc.After doing the necessary actions cliock ok at the end.Now go back to the
document library page and upload  a document your field will be there and you can
fill in the details.Similarly for other fields you can repeat the steps.
regarding your second part for adding these fields as the search  criteria i
will tell you later.

If you are talking about Office properties then you need to create
custom columns in the document  library. The names of these custom
columns should match the custom  properties in your Office document. Then
when you upload  these custom properties will be promoted into the
columns.

Note this promotion does NOT work for inbuilt Office properties (except
Title) only custom ones. Also the promotion does NOT work when you
upload through the browser (which is a bug!). You have to either ruse
the Web Folders interface or save as directly from the Office app.

you can only do this on a document  library
level, not a site level (not sure what tags  you would be referring to at
a site level anyways). Just select the document library and click Modify
Settings and add/remove/edit columns. With Office documents  these are
syncronized and will create custom  properties in the document itself on
upload.

I have a fairly lengthy blog here on the subject:

weblogs.asp.net/.../267846.aspx

I was thinking that maybe at site level there could have been a
functionality which groups together meta  tags and a one point access to
change the meta tags  for all the document  libraries under the TLS. But
now I know it isn't so.

Thanks for the help guys. I explored couple of possibilities.

* I used the backward compatible document library component in SPS
2003 to get a different looking document library on my portal. This
allows me to manage document profiles and grouping of Meta tags in these
profiles. But it creates a separate area in my portal for document
library. And I am not sure whether it allows me to create more of such
document libraries. Clues?
* I used custom  columns in document libraries in my searchable WSS
sites and added text explicitly to these custom properties.

The problem for both of these approaches is that the advanced search  on
custom properties works only for office documents  and not on .txt or
.gif files (yes, I included the custom tags in advanced search). But if
I put the custom property value in the simple search box, I get the
results!! (even non-office documents). I then explored further and saw
that another property is created named ows_pppp where pppp was my
original property name. Included it in advanced search and presto! got
my txt and gif files in search results. But why does it happen? I have
no clue. Maybe I can map ows_pppp to pppp, but it's a workaround.

I didn't figure out one thing though. When I say that include property
"x" in advanced search. How much time to I have to wait before it
actually appears in the advanced search dropdown. What drives it? I
usually have to wait around 15-20 minutes, but I don't want to wait that
long.

Indeed, there is a third party search  vendor for SharePoint which
handles metatags/custom fields/doc properties OOTB: Coveo Enterprise
Search for SharePoint lets you search on custom  metatags, columns in
doc lists/libraries, etc. In fact Coveo allows typing of metatags,
parametric search, and sorting. Coveo works for both SPS and WSS. We
don't stop with custom metatag handling; we add another 50-70 features
and capabilities