(The post name is there for a few buddies to laugh at. Move on...)
BSNES did an update while I wasn't looking (not that I look that often anyway..)
Satellaview ROMs now cause an auto-prompt for a BIOs cart to appear - this replaces the old "Load Special" option from the old versions, and renders my old guide obsolete. On the other hand, now it's likely easier to figure out than it was before - just load your ROM and then pick the BIOs when prompted.
Slotted carts work in a reverse manner - pick the main cartridge first, and then pick the Data Cart that goes with it when prompted.