You could try re-directing the output to the nul console by adding > nul:

select @cmd ='C:\"Program Files (x86)"\"Microsoft SQL Server"\90\DTS\Binn\DTExec.exe /DTS "' + @PackageName + '" /SERVER "' + @MachineName + '" /MAXCONCURRENT " -1 " /CHECKPOINTING OFF /REPORTING N > nul'