how do i download music to my computerHow do I transfer music from one computer to another?

I recently got a new computer and I want to transfer my entire iTunes library to my new computer. However, there are a few small problems that are not allowing me to do this.

First, not all of my songs were purchased off of iTunes. Some were, but many were downloaded from albums I personally own, YouTube, torrents, etc. This means when I try to transfer it directly via my iPod, ithow do i download music to my computer only transfers the portion of the songs that were purchased through iTunes. Not helpful.

Secondly, many of the songs I downloaded were not in the format I wanted them in when I downloaded them, so I changed album artwork, lyrics, titles, etc. within iTunes after they were downloaded. This eliminates my option to just transfer the original files via an external hard drive, becausehow do i download music to my computer the original files are much different than the way they appear now.

Is there any way around these two problems above? I just want to put all the songs on my current iPod onto my new computer, but can't due to iTunes' "you can only put music downloaded through us into your library" philosophy. Help?
Plug ur iPod in the new computer and everything should be there