I use my Compaq Presario to run Cakewalk. I edit and run my MIDIs from there to a SC88, which then is sent to the mains. I use the audio out jack to play mp3s. If you use a parrallel MIDI interfacea USB or a "to host" connector to your arranger, it will use the Yammy's internal GM/XG sounds to play the MIDIs, but you will have some limitations in using your keyboard concurrently, SO you might want to have a second keyboard for playing OR use a sound module like te SC88, MU50, EM100, etc. If you have Windows98 or higher you should be able to use the "GS Wavetable Synth" as you soundsource - it's basically a Roland VSC engine.
------------------
Cass Pawlowski - Motown
PSR2000, SC88, Cakewalk