Why is the Toshiba drive set to hdb while booting, but the /drive1 comes from hdc?
Because we cheated, to make things the same between Mark 1 (which has hda and hdc) and Mark 2 (which has hda and hdb). The second drive in a Mark 2 "is" hdb, but the device nodes /dev/hdc* are the ones which would normally refer to hdb.
no room for private writable mapping
You should enable swap ("swapon /swapfile") before running fsck, you'll get out-of-memory errors like that one otherwise. However, that's not your main problem; it couldn't cause those IRQ errors. Either the second drive is failing, or --
much more likely -- there's a problem with the IDE cable, perhaps where it's attached to the second drive. Dismantle the player and check all the connections are bedded-in properly.
Peter