I think these programs are similar if I'm wrong please correct me.
but if not please let me know which one is easiest to use and is not too expensive. I don't know that much about music computer programs so I'd like some help.
Logic and Cubase are similar to each other, they are the top of the range sequencing and digitial audio programs.
Garageband is a Mac only application, kind of like a budget digital audio program, but there are a stackload of pre programmed loops available that work really well in Garageband (you have to pay for most of them though).
Band iN a box - whilst I think you can record with it - is more of an auto-accompaniment program. You can type in a chord progression, choose a style, and BIAB will generate a track you can play along with.
All of them have their pluses and minuses.
Depending on what you're trying to achieve will affect which one is best for you.
Post what you want to do and I(and others) can advise you which is best...
Logic is also Mac only. It shares some common code with Garageband, so if you get the right versions you can move files between the two. Apple run them as a three tier system: GB for the casual user:Logic Express for the serious hobbyist:Logic Pro for full commercial users (though of course how people choose to use them is independant of how Apple target them). It's the same for video: iMovie, Final Cut Express and Final Cut Pro.
I've got GB and Logic Express - GB is a LOT easier. If youv'e got a Mac then there's no reason not to use GB until you outrgrow it, and then move up to Logic Express (and if necessary to Pro). upgrade pricing is good, so I picked up an older/discounted version of express really cheap, and if I ever need the newer version and/or the pro version I'll still be ahead of buying the full version outright.
something to jam with
make practice a bit more interesting
write songs with
use it to record a demo to give to other musos
something easy to use
doesn't have weird sounding midi for instruments
not too expensive eg. over $300Australian
Runs on windows XP
Can change files into mp3 format or something so I don’t have to sit near the computer to jam
Would be useful as a teaching tool(my friends thinking of going halves, she’s a guitar teacher)
But from what I've heard on these forums it's probably “band in a box” I'm looking for, but I'm not sure, so I need some help.
The price thing pretty much rules out Cubase and Logic - both of these are quite expensive. Also Logic and Garageband as Ian pointed out are Mac only applications.
So that leaves Band In A Box. Here's what boxes it ticks...
something to jamwith
]You can jam till the cows go home with Band in a box. In all sorts of ways. Chord progressions. Songs. Different styles. Only limit is your imagination.
make practice a bit more interesting
On its own BIAB won't make practice more interesting, you need to do that with how you structure your routing. THough as point 1 there is SO much you can do.
write songs with
You can. Or BIAB can write 'melodic sketches' for you based on chord progressions in its memory banks.
use it to record a demo to give to other musos
Hmmmm - depends on the quality of what you want to give to other musos. If you want to give them a high quality 'working' demo then probably not, if you want to give them a sketch of the song for them to work on and use their own 'creativity' then yes.
something easy to use
doesn't have weird sounding midi for instruments
BIAB DOES have midi instruments - and some of the programming is a bit clunky. (Some of it is pretty cool though). They've also started incorporating what they call REAL BAND - which are effectively live loops into the program which are much better sounding - but these add ons do cost.
not too expensive eg. over $300Australian
The basic program is around US $120. (Add-ons will take you higher though)
Runs on windows XP
Definitely runs on Windows.
Can change files into mp3 format or something so I don’t have to sit near the computer to jam
You can export files to MP3.
Would be useful as a teaching tool(my friends thinking of going halves, she’s a guitar teacher)
I've never used it as a teaching tool per se, though I've used tracks and files I've generated in BIAB to give to students to practice with.
But you probably could as it's got a fretboard view (though I've got to be honest I've never used this feature).
Hope that helps you make a decision.
The other option is a cheaper DAW application (I'm sure there are cheaper versions of programs like Cubase, though off the top of my head I can't tell you names as I use LOGIC myself)
Music software 
