For Quick guitar parts, it especially helps to slow the playing speed in windows media player while transcribing from an mp3!
For solos, adjusting the panning control on the computer to Left speaker only (or right speaker only) will separate guitar parts if a band has a lead and rhythm part overlapping. It can be really tough otherwise, especially when the guitars play overlapping/counterpoint melody or harmonized passages.
Knowing scales and modes helps too. Try to figure out the major scale that your solo notes fall under, since the solo may be based from any note on the scale. This will help you know which notes would be played and in what frethand position the guitarist is playing on the neck.
If you have a question, send me a message or comment.