Right now I have a Song Viao PC, pentuI'm 4 processor, 250 gb.

I have songs in my head. I don't play any instruments.

1. I would like to first hum the songs into a microphone and have that basically converted into notes on a page with an audio to midi conversion program.

2. I would also like to have the music notated on my computer screen where I can move the notes around with a mouse.

3. I then want to convert those notes into the instrument of my choice, ( I understand midi is the way to do this, or
The instruments of my choice are the most realistic sounding as possible instruments of, the symphony orchestra and also the rock n roll and metal ensemble guitar,metal guitar, bass, drums. I don't care about dance beats or loops,maybe drums on a loop would be okay if it could be varied.

4. Also a sound card for these purposes.

I want to minimize the amount of software I have so if I could buy a recording program that was geared toward these kinds of music that would be best I'm thinking. For instance I read that audio to midi conversion is possible with Logic pro 7?
I have read that guitar sounds are cheesy and fake sounding as midi. I have personally only heard really cheesy samples on the net. Which software offers the most realistic sounding guitar?
I plan on buying everything over ebay.
Thank you for your help. I would have liked to continue to read more but I can't wait any longer to buy some gear