Hi Grace,
I imagine you have an orphaned user - take a look at sp_changeuserslogin to see one way to fix it. Aliases are out dated - in 7.0 and higher you normally just use roles.
To see if the db is still being used, one way would be to set it to dbo only and see if anyone complains! Another way would to use Profiler to trace activity related to that db.
Also, there is a check box on the posting form where you can elect to be notified when someone replies to your post.
Andy