Synapses crackle -
Take a soft synth package like propellerhead's REASON 2.0 ($280?) http://www.propellerheads.se/
ADD
One 'Desknote' Laptop [upgradable memory AND cpu!]
ECS A929 i-Buddie XP ($650 - 790?) http://www.sybercom.com/cgi-bin/sybercom/NBA929C
ADD
One USB / MIDI Keyboard controller ($250)

Result - one powerful portable workstation / arranger, that has storage capacity, great sound output, and expandability.