I had tried something similar - created a new account, gave it the necessary
permissions to the SQL databases, put it into the "Sharepoint Administration
Group" that is set in SPS and added it to the Local Administrators group  on
the web server  (I did see if I could narrow it down to specific user rights,
but none of these seemed to work). I amended the account  to use for the
crawl and this worked - the crawl completed successfully.

I then added the original account to the Local Administrators group on the
web server, changed the crawl back to use the default  account and...

it still didn't work :-(

Yet, this account appears to be correctly working  for the rest of the portal
& the Application Pool!!!???