Okay,
I'll tackle this one.

" I've read in the forum about DXi vs. sound card, still am not sure if I need a sound card, or just DXi, or sound card AND DXi."

'For $1,000 Alex, 'What is the difference between a hardware component, and a software synthesizer?''
DXi and VSTi are names given to software synthesizers. There are others, such as RTAS for Pro Tools, and probably a few more. VSTi and then DXi are probably the two most popular. A synthesizer is any device that creates a sound, in this case, a musical note in response to a specific input. The DXi and VSTi are software, meaning that it's all done in software. BUT, it needs some hardware to actually be heard. This is where the sound card, or sound chip on your motherboard comes in. The sound chip converts the information from the software synth, and turns it into analog voltages which will drive a speaker, amplifier, or headphone, i.e., 'sound.' For the most part, a DXi without a sound card is useless. There are some exceptions to that rule, but for the most part,it stands true.

Now, you can purchase a hardware synthesizer, such as a keyboard workstation, which combines the midi inputs, the software, and the sound card all in one device. Press a note, hear sound. Some even come with built in speakers, so you don't have to hook it up to an amp.

A MIDI controller is a 'dumb' keyboard, no internal sounds of its own, and sends MIDI data to a synth, either software or hardware.

" From what I've read, writing chords and melodies from the laptop keyboard looks like a lot of work. I'd like to get a simple midi keyboard to "play in" (to BIAB) melodies and chords, not sure what's best."

Melodies, you can do that, chords, you can not. Band In A Box, as part of what it is, requires that you input the chords in a step sequence, usually by typing them from the keyboard. It's not hard, it's fairly quick, and in the end, to me, it's a lot easier. It's also very easy to change out a single chord, if you wish to make some sort of substitution.

You can, however, record input from the keyboard for the melody. So, if you're playing a song with five parts, i.e., Drums, Bass, Guitar, Piano, and Strings, and you wish to add a melody, type in the chords for the song, find a style you like, and make sure it sounds okay, then press the 'Record' button, and record the melody line in from the controller keyboard/wind synth/guitar/whatever you're using.
At that point, you can mute whatever part you wish to allow your student to play along. Band In A Box will regenerate the parts each time, so they'll be different each time you play the song.

" I would really like a professional sound; a too "synthesizer-y" sound will drive me nuts."

Pro sound requires pro dollars, for the most part. Two ways to get around that. First, buy the SuperMegaUltra Pak, or whatever they're calling it these days, that has the full set of Real Drums and Real Instruments in it. At this point, you can generate BACKING tracks with the Real Drums/Real Instrument tracks, but they are still limited in style and scope at this time.
Band In A Box is 'General MIDI' based, meaning that you'll need to have a synth capapble of GM sounds. Which, today, includes about every one of them. But, let me say this, the concept that General MIDI sounds are horrible is false. It is possible that a manufacturer will take the absolute best data they can use and create a bank of General MIDI sounds that will blow you away. The problem with that, for the manufacturer, is if you do that, how do you sell the other sounds on the synth.
For the most part, synths like the Roland VSC DXi, or other software synths, IN MY OPINION, do not stand up to a good hardware synth. But, then the question becomes, how much do you want to pay for a good hardware synth? Five hundred, $1,000, or maybe $2,000? How about $3,000 or more? All of that is available, and all reflect different concepts of what a 'good synth' is.
I use an Arranger keyboard, a Korg PA800.
Listen to some of the demos of this keyboard here: http://www.korgpa.com/pa_root/en/products/pa800_demo.html?en

Street price on this unit is $2,800. But, the sound is nice.

However, that may be a bit rich for your blood. However, you *can* get a 'sound module' which is the sounds, a couple of connectors and the output for a few hundred dollars. In fact, PGMusic sells the Ketron SD2. You can demo the demos of the SD2, SD4 and SD5 (all of which use the same sound set) here:
http://www.ketronus.com/demos.php One of those, for $379US and a 61 key MIDI controller like this, http://keyboards-midi.musiciansfriend.co...ller?sku=703607 for $200 will give you a sound that *is* professional, and won't sound too 'synthy-ish.'

If you want to record the audio outputs from the synth into your computer, you will need then to get an interface for the audio (you'll need one for the MIDI anyway) so that you can record. The sound card in your laptop is not going to be up to the task, but there are many different available devices you can purchase for a relatively minimal cost.
This works well for the MIDI interface: http://www.pgmusic.com/um1ex.htm
This will work well for the audio interface: http://www.pgmusic.com/ua1x.htm

Combined, those two units, along with the Ketron SD2, the 88 key controller, and the Band In A Box Ultra Pak, with 80GB USB hard drive http://www.pgmusic.com/bandbox.htm will give you a fantastic combination that will allow you to present to your students completed works for them to play along with and study from.

Finally, something else that very few places will give you is this...a team of knowledgeable, willing, friendly users in a forum who will take the time to walk you through, step by step, what it will take for you to get from 'techno-ignorant' to producing CDs.

Gary

I'm blessed watching God do what He does best. I've had a few rough years, and I'm still not back to where I want to be, but I'm on the way and things are looking far better now than what they were!