Andrew,
It sounds like you found the job owner specification and that is not the problem (let's hope). A quick search yielded some more specific details about running the DTS package as a job and the differences between the two. I've extracted the appropriate content from their sources:
From:
http://www.databasejournal.com/features/mssql/article.php/3404791
You can also schedule execution of DTS packages using SQL Server Agent jobs. This ability is granted by default to the public group, based on permissions to execute sp_add_job and sp_add_jobschedule stored procedures in the MSDB database (this applies to all SQL Server Agent jobs, not just the ones that invoke DTS packages). Typically, it is recommended to restrict access to them to a limited number of privileged logins. While jobs typically execute in the security contexts of their owner, in the case of DTS packages this might be different. The reason is the fact that a task that contains invocation of a DTS package accomplishes this by the running DTSRun command line utility, which involves, in turn, the use of CmdExec. If you limit permissions to launch CmdExec jobs to members of the SysAdmin fixed server role (which is the default behavior), jobs will still execute in the same security context as their owners. However, you can change this default in the SQL Server Agent Properties dialog box, accessible by selecting the Properties option from the SQL Server Agent node under the Management folder in the SQL Server Enterprise Manager console. In the Job System tab, you need to clear the checkbox next to the "Only users with SysAdmin privileges can execute CmdExec and ActiveScripting job steps" and provide a Proxy Account name and password. The proxy account provides the security context for execution of DTS packages, so ensure that it has access to all relevant data stores, file system paths or COM components, which might be used by ActiveX scripting tasks. Remember, however, that at the same time you allow users without SysAdmin privileges to run potentially dangerous ActiveScripting jobs.
What further complicates scheduling DTS packages is the fact that content of the corresponding SQL Server Agent jobs includes SID of the SQL Server Agent account as part of the encrypted string passed to the DTSRun command. This creates a problem if the password of the SQL Server Agent account is changed, since it forces you to recreate each package (existing packages will fail due to password mismatch). Also, keep in mind that the SQL Server Agent service needs to be running in order for scheduled job to be launched.
From:
http://support.microsoft.com/default.aspx?scid=kb;EN-US;269074#E0PD0ABAAA
Common Problems
Here are a few other common problems you might encounter when you run DTS packages as scheduled jobs in SQL Agent:
Mapped Drives
If the package relies on the physical location of a file designated by a mapped drive letter, the package may fail when it is run as a scheduled SQL Agent job, regardless of who owns the package. SQL Agent is a Windows NT service and Windows NT services cannot see mapped drive letters. The mapping is part of the user's profile that is loaded when a user logs on to a Windows NT session. Services do not work with user profiles. Use a UNC path instead of a mapped drive letter. For additional information about why a service cannot use a mapped drive, click the following article number to view the article in the Microsoft Knowledge Base:
180362 (http://support.microsoft.com/kb/180362/) INFO: Services and redirected drives
Relative Path
A relative path (or drive letter) is specific to the current location of the package (like C:\). If a package is designed on a workstation and is then scheduled, the location from which the package is run changes. The drive letter paths now reference a different physical location, that of the server. Unless the referenced files are also moved to the server, the package execution fails.
COM Components in ActiveX Scripts
If COM components (for example, calls to Microsoft ActiveX Data Objects (ADO), Remote Data Objects (RDO), or Decision Support Object (DSO) objects) are called in an ActiveX script, the called components must exist on the computer from which the DTS package is being run. If you run the package from the DTS Designer in SEM or DTSRun.exe, the components must exist on the computer at which you are seated. If the package is scheduled to be run by SQL Agent, the called components must be loaded on the computer hosting the SQL Server.
Package Security
DTS packages can have owner passwords and user passwords. These passwords affect who can edit and run the packages. Neither of these affect the security context in which the package is run.
SQLAgentCmdExec Permissions
If the job is executed under the context of the SQLAgentCmdExec account, and the SQLAgentCmdExec account does not have login rights to the SQL Server, the job may fail with the following error message:
DTSRun: Loading... DTSRun: Executing... DTSRun OnStart: DTSStep_DTSExecuteSQLTask_1 DTSRun OnError: DTSStep_DTSExecuteSQLTask_1, Error = -2147217843 (80040E4D) Error string: Login failed for user 'NT_name\SQLAgentCmdExec'. Error source: Microsoft OLE DB Provider for SQL Server Help file: Help context: 0 Error Detail Records: Error: -2147217843 (80040E4D); Provider Error: 18456 (4818) Error string: Login failed for user 'NT_name\SQLAgentCmdExec'. Error source: Microsoft OLE DB Provider for SQL Server Help file: Help context: 0 DTSRun OnFinish: DTSStep_DTSExecuteSQLTask_1 DTSRun: Package execution complete. Process Exit Code 1. The step failed.
You need to grant the SQLAgentCmdExec account proper login and database permission rights to the SQL Server.
--Eric Swanson
http://www.ericis.com/