SharePoint - SharePoint 2003 enter credentials over and over

Internal users are fine but for an External domain users (there aren't many)
to have access, I have Local accounts on the box mapped in IIS to local
accounts and digital certificates stored in a local directory. When users
goto a sharepoint site and click on documents in a library, they are prompted
to login to open the document - which they do and it opens fine..... but,
let's say they want to open another document after the first, as long as Word
is open, they open the next document fine - however, if they do the same
thing (login) open a document and close out MS Word, then try to open another
document, they are prompted to enter their login credentials again and again
even though they are logged into the site - how can I prevent this from
happening? Thanks in advance.

ny)
pted
Word
ther
ain

AFAIK you can't. It's a known issue. It's not really SharePoint it's
an Office dll that's the problem. When Word fires up it wants to know
who's starting it so that's fine on the internal network but not off
it where the app pool account is the only thing it knows about. That's
why its not a problem with Word already open because it done its
authenticating bit. The only way you could try to get around this
'double hop issue' would be to switch everything to kerberos
authentication which would allow the users credentials to be carried
through. Even then, I wouldn't guarantee it.