For why to keep the "Archived" media sets. As long as the tape volumes are in one of these media sets, and as long as the OPP of that set is "Infinite - Never Overwrite", Backup Exec will NOT overwrite that tape, so the archived data is safe and available.
If you get things working the way you want and don't want to start from scratch, see http://support.veritas.com/docs/260054 to move v9.1 to the new server, then upgrade in place to v10d
For your two media sets, I'd set OPP to
Weekly 209 days (30 weeks, minus 1 day)
Daily 13 days (2 weeks, minus 1 day)
(I use the minus one day so that if the job finishes after midnight, the volume is still overwriteable the next time it is due to be used.)