added specific handling for a few errors we were seeing against SQL Server 2000.  2400, 20020, and 20047 all cause db-lib to bail out and we were seeing 500's at the apache level (not getting raised up to rails).  this would also result in the death of our webserver processes and no new results would get served until after a long timeout.

i'm sure there is a better fix than this, but this has already improved things significantly