The wk3000 or 3500 are the 2 keyboards I know about. You cann't export a 'song file' (Casio's internal sequencer format)...out of the keyboard as a midi file. This is because it contains commands to activate parts and variations...that are exclusive to the Casio. You can record your song (as you play it live)...to a computer based sequencer (like PG Music's Power Tracks)...and edit and save it as a midi1 or midi0 (also known as a SMF file)
The SmartMedia card can be formatted in the Casio's card slot. Then move it to the computer's card reader/writer. You can load in the SMF format files directly to the Card...from any computer. The SMF format reffers to all the 16 mid channels being on 1 sequencer 'track'. A midi1 format (most common)...has 1 channel per 1 sequencer track. (think like a multi-track recorder for midi1...and a single track recorder for midi0). Most all computer based sequencers can convert between the 2 formats.
The bummer for Mac users...Casio doesn't have a mac version of it's software. The Rhythm/tone files you can download from Casio are mainly 'ckf' format. You need the software to convert them to the 'z0x' file format that the Casio really wants to see. We are trying to post the files in the 'z0x' format on the Pianoman's web site: http://www.originalz.com/casio/casio_bbs/
These can be loaded directly to the SmartMedia card, using a Mac...then loaded into the Casio. If you have a pc emulator program...it might work with the Casio software. The Software has the ability to convert midi files into 'Rhythms' ...(with lots of effort). But, it does work.
Sorry, I cann't help on the other keyboard.