Joe . . .
Thanks much for your reply -- you gave me the idea about trying to log into the server using the connection string credentials. It failed which led me to a SQL Server 2008 troubleshooting session. One of the problems (embarassingly) was that I had the Authentication Mode set to Windows only, not Mixed Mode. Then, after fixing that, I learned that the User credentials also failed. So, after going to mixed mode, ading a new Login and User and then fixing the Connection String, I'm in business.
Lesson learned (and I know better) - never take error messages literally. The real, basic problem WASN'T the connections string after all.
For anyone who's interested here's a little more detailed info that led to solution.
When I attempted to connect to SQL Server using Management Studio and the uid and pw I got the message that the Login failed for that user Error 18456 State 1. Trouble is that State 1 isn't the whole story and you have to go look at the SQL Error Log to find out that it was really State 58 (in my case). The log told me I was in Windows Authentication only. So I had to change the mode and then, IMPORTANTLY, stop and start the SQL Server service so the change would take effect.
After doing that, the login using my original credentials still failed but for a different reason -- that user wasn't found. The Error Log also told me that. So I added a new Login and then aded it as a User for my DNN database, changed the credentials in the web.config connection string (2 places) and SUCCESS. My site runs on localhost.
Thanks again for pointing me in the right direction!
Al