The only PCMCIA solution for SCSI devices is/was Squirrel SCSI (last version is called Surf Squirrel).
IDE drives are cheaper, but u need an IDE cable to the outside and set the CD as slave.
With an original (or unacelerated) A1200 you'll never be able to play MP3, not a single one. Not enough CPU power.
Get an acelerator (at least a 030/50MHz) with a lot of memory (32 Mb or more) and you can do the trick. Better with 040 or 060, even better with a PPC acel.
