flop evaluation in book: small stakes hold 'em

Hi,
I am just working my way through "Small Stakes Hold 'em" and would like to know more about the hand evaluation after the flop:
a) Is there a rating system by which the hands are evaluated? For example: Hand A and hand B are both rated "strong hand", but hand A is better than hand B. Why is that so?
b) Are these hand ratings valid for small stakes only? I could imagine that drawing hands are less valueable in higher limits with less opponents.
c) Are there other factors not mentioned in the book influencing the hand value (i.e. position)?

Thanks for your time!
Thrakkar