Exactly what I was looking for. I needed a path for automated tracing that the sql agent account had permissions to, and not dump everything in the root of C:\ like my predecessor in SQL 2000. It works on my multiple instance machine SQL2008.
I added the following to get the default errorlog path
SET @path = NULL
exec @returncode = master.dbo.xp_instance_regread N'hkey_local_machine',N'software\microsoft\mssqlserver\CPE',N'ErrorDumpDir', @path output, 'no_output'
Thanks a bunch!