I will reinforce the points made here.
You are going to "learn" little from trying to maximize the use of the mic "that came with my soundcard". The frequency response is horrible. The SPL handling is horrible. And the proximity effect will drive you nuts!
Just about ANY XLR type of microphone is going to be better friend.
Look at a Shure SM-57 or 58. The 57 is about $80 new, and the 58 is only about $10 more. While neither would be my choice, in a pinch for recording a demo, I would favor them over what you have any day of the week.
Getting into the whole recording things requires a bit of a commitment to at least have equipment that is somewhat usable. The mic you have is truely not at that level, unless you seek a messed up sound for a special effect on a track.
Another little bit of advice:
I would shy away from ANY processing of classical guitar. If because of using a less than desirable mic you need to eq a bit, try not to do anymore then +/- 3dB of eq. Any more than that and you start really altering the tone of the instrument in unnatural ways, which I don't think would be desirable for a nylon string acoutic guitar.
I used to have a recording by Kimbal Dykes (some Canadian dude who did a lot of Bach) and they used some reverb on the guitar. Truthfully, I didn't like the sound. The guitar sounded great, but the reverb sounded a bit unnatural. I have NEVER heard an
acoustic guitar sound that way in a room before, and this sort of distracted me in the listening of the otherwise fine playing.
Buy a another mic. There is little any here can suggest in the usage of the mic you currently use. It is just simply that bad of a mic....
Ed