In Excel, I can import external data from

Data | Import External Data | Import Data | New Source

Where you get the Data Connection Wizard.

One option there is "Microsoft Business Solutions" where you'll get
a dialog box that says:

Type the computer name or URL where the data retrieval service is
located. Typically a data retrieval service is located on a server
running Microsoft Windows SharePoint Services 2.0.

So I enter the URL of my portal:

http://myportal

and I get this error:

The appropriate data retrieval service could not be found at the
floowing URL: http://myportal/_vti_bin/dspmbs.asmx. Reenter the URL
or comuter name for the server and try your request again.

Where do I get one of these dspmbs.asmx things?