Noise pick up from mic

by Bala
(Chennai,India)

I am using an un branded mic and use with my PC.The recoring quality is poor. It picks up the hum and other atmospheric noise. My questions are:

1. Which type of mic to use? - Condnser,crystal etc..
2. Will using USB mic reduce the noise? If so which type?
3. Any particular brand?
4. What is the compression technic/tool that I can use that would reduce the audio file size.