First, a bit about my own experience in music. I started playing violin in fourth grade, thanks to my school district's awesome music program. It turned out that I had a certain knack for violin, so at the suggestion of an All-State judge, I started taking private lessons. Along the way, I also taught myself a fair amount of recorder (and not just soprano), a little bit of flute, and was shown the basics of cello and double bass. Violin is definitely my primary instrument, but I put "making music" whenever people ask my hobbies, because there are a lot of other instruments involved.
Now, on to the various ways that someone who's a not a music major, or even a Conservatory student, can still make music at Oberlin. These are listed in no particular order, just in case you're concerned that I'm exhibiting bias.
Option Number One: ExCo's As mentioned before, I've taken the Music of North India ExCo for the past two semesters. The ExCo is taught by a very qualified, very talented woman. Generally, she teaches sitar, tabla, and voice; however, there are a few students who take private lessons with her on other instruments. These range from other traditional Indian instruments to Western ones, like my violin. I take lessons with a violist, and there is also a double bass student, who is very, very good. The lessons are fun, and a completely different style of music than anything I've experienced before. I've taken a slightly different route with these lessons--there's no prior experience necessary, unless you want to take the route that I have.
This isn't the only ExCo involving music. One that I've had my eye on for a while now is a program bringing music into the local elementary schools, but this little thing called time has prevented me from exploring it so far.
Option Number Two: Winter Term There are several different organized Winter Term projects that involve music. I haven't participated in any of them, but they look very interesting. Want to make your own banjo out of a gourd? You can do it. Want to be part of a gamelan ensemble? You can do that, too. And of course, if none of these options really appeal to you, you can always create your own.
Option Number Three: Ensembles There are quite a few large ensembles to pick from, if that's your sort of thing. I am a member of one of them, College Orchestra (recently re-named Oberlin College Symphony). It's a student-run orchestra comprised entirely of students from the College with the occasional composition major thrown in for good measure. It's a great, low-pressure ensemble.
There are also two other ensembles specifically for College students: College Community Strings and College Community Winds. As the names suggest, the former is a string orchestra and the latter is a wind ensemble. Both are conducted by faculty members from the Conservatory.
Besides these, there are other opportunities--you just have to find them. I've had the chance to play for several pit orchestras, most notably for OGASP (Oberlin Gilbert and Sullivan Players). I've found that it's not so hard to find a pit orchestra to play for, even if I'm not a Conservatory student.
Option Number Four: Secondary Lessons One really great thing that the Conservatory offers for non-music majors is the opportunity to take secondary lessons. After an audition (which, take it from me, isn't as scary as it sounds), you're assigned a teacher. In my case, I've had two great teachers, both Conservatory students. Depending on the instrument, you may be assigned a student or a faculty member as a teacher. If you are assigned a student, you still get chances to play for a faculty member.
Option Number Five: Small Groups Finally, with a lot of people who play instruments, there is always the option to form small groups, both formally and informally. Again, I haven't taken advantage of this, mainly due to the time issue. However, one of my friends, working with another student, rehearsed and performed an arrangement of Stravinsky's "Petrushka" for two pianos. They received coaching from a faculty member, though only one of them is a Conservatory student, and put on a very nice rehearsal at the end of the year.