holla!
do you already have a good midi-keyboard to trigger the rackmounted asr? if so, then go for the rack..
if you don't, then go for the version with keys..
but i'd strongly recommend trying software first.. (i.e. FL Studio, Reason), see how u like it, learn the basics, learn the effects and how to use 'em, and once you feel comfortable with everything go get your first piece of hardware..
if you already know that you'll be going the hardwareway at one time, then i'd recommend "reason", because it's closer to a "real" setup. (you'll see what i'm talking about, once you've seen its graphical interface)
easier is fruity loops tho, and with its ability to use vsti-plugins (not possible within reason, but there are lots of "refills" available) you can load some very nice instruments in there (the included sounds don't sound pretty good, and/or you'll get tired of them really soon
)
both are great programs to start out with, even tho there'll be a higher learning curve in reason and, as i already mentioned, you'll also get a hang of how to use hardware easier like that