Much of the music nowadays is done in what is called "work for hire", this allows studios to own much of the rights to the music (depending on the agreement you still retain writers credit, and a few other rights).

grad students have very little to no money, so you can most likely attain all the rights to the music and get an agreement worked out to get some cash if its picked up and distributed, you can also register the music with different musagencies to track it, tho I think you'll have to ask someone more in teh film biz than me (I do mostly short animations and video games)

Software choices really depend on the style of music you're going to go for. What you have is great for some live recordings. POssibly an acoustic guitar score, and some electronic pads manipulatd in real time. You can get a very "organic" sound.

I'd personally set up a PC of some sort and get Gigastudio or Kontakt (PC version is better), these samplers can stream large orcehstral samples of the hard disk. Problem is you'll also have to buy some orchestral libs if you want to do orchestral work. The good ones are fairly expensive.

If you have a small budget look into picking up either Garritan Personal Orchestra and/or East/West-Quatum Leap Symphonic Orchestra "silver". Which is the lightest version o ftheir "full" library.

If yuo have a bigger budget. Check out the Vienna Sympnohic Library. Opus 1 is a great start. The Pro Series is phenomenal

as is the E/W Quantum Leap SO "full" version.

Also if you do plan on doing some orchestral sequencing, I'd suggest a good sequencer like Logic or Cubase. PT doesn't have that much in the way of MIDI tools.

Outside of orchestral stuff, you might want to look into apps like Acid for the PC. This is a loop manipulation softare, that far exceeds the control you get in recent MAC apps like Garage Band and Soundtrack in FCP. Its vry flexible and very quick to work in if you are working with loops of music.

Regarding the adaptation of previously existing music, unless you have a decent budget to license it (or it is public domain), don't do it.

I am a filmmaker myself, and I have worked several times with a composer. I find the most difficult aspect of the whole process is communicating with the composer what sort of approach you want to take without blunting his creativity.

The way that I do this is that I give the composer a CD of music in the tone of what I'm looking for. This will allow them to get the idea without getting too specific. Hopefully, then they can go their own way, but still provide for me what I am hoping for with a film.

Since it is difficult to show a film without a temp track, I always prepare a music-less version of the film for reference purposes. When I show the film to the composer, however, I tend to show the version with the temp score because I need to give them an idea as to what I think is needed for each scene.

I prefer to work with a composer when a cue isn't working rather than edit other cues. I couldn't do this at one point because of tension between myself and the composer I was working with at the time, but once everything calmed down, I showed him what I had done to make sure that it was okay with him. He asked me to make a slight change, but appreciated how I handled the cue.

I have generally worked pretty closely with my composers (back in the olden days of analog recording I would run the four-track for acoustic instruments), but I am aware that communication is a difficult thing for filmmakers. Most of them know what they like, but don't know how to express themselves musically.