There is nothing to do this OOTB, as this is an SPS function which is not
available in WSS. You could write a custom search  web part that would make this
available on WSS sites hosted on a server running SPS, but it will require some
level of coding.

At the technology level, WSS only uses SQL Server full-text searching (hence
the WSS limitation of only being able to search  WSS the sites within a
particular site  collection (aka WSS SQL Server database)).

SPS 2003 ship with the full-blown MS Search platform that enables an SPS
portal to index and search any content - almost regardless of where it
lives; for example, SPS portals, WSS sites, crawled web sites, Exchange PF,
Lotus Notes databases, file shares, etc.

I have found these three articles useful:

www.msd2d.com/.../Tip_viewitem_03.aspx
b95a-d5bc916f1597

msdn.microsoft.com/.../SearchGET.asp?frame
=true

msdn.microsoft.com/.../ODC_SPSSearch
BoxwithPortalSearchResults.asp?frame=true

I know the advanced  search capability  is only available at the portal
level and not at the site  level. Is there anyway to modified the drop
down lists when doing an advanced search? I have created several
metadata fields associated to the document libraries at the site level
but when I go to do an advanced search, these fields are not included in
the drop down lists for either document libraries or documents.

You need to manage index properties (from Site Settings on the portal).
In here you will be able to find properties that have been indexed
ordered within namespaces. Can't remember the exact namespace for custom
properties but I think it ends in :office !

In here your custom property will be prepended with OWS_. Therefore if
you have added a field to a document library called, for example, amount
then you will have a property called OWS_Amount. You can now select the
property and set some details on it - one of which is "display in
advanced search". It takes a short while for the change to replicate to
the portal...

We have one particular Team site  that will not index properly with
their corresponding metadata fields. Here's the scoop! I've checked
the Approved Sites to Crawl list (under configure search  and
indexing) and all crawling functionality seems to be on schedule.
However, when I go to Advance search (at the Enterprise level) to
search specific metadata (only from the one site) , I get no results.
Other Team sites are searchable via the advance search function but
not this particular one. Any ideas?

Have you checked the indexer logs to make sure the team  site is being indexed
correctly? Are you doing the search  as a member of the site? The user needs to
be explicitly added as a site  memeber - admins that have access but are not
members don't show search results.