I've never actually read one of these before, but having a substantial dating past, I will now give my two cents to be flamed later on:
Nice Guys? are dastardly bastards who are only hiding their insecurites. Nice guys are people who wear their insecurities on their sleeve.
The answer is, be genuinely respectful to members of the opposite sex. But don't think you can be a Nice Guy? or nice guy and be an insecure little wretch. Confidence is all that matters. What about you makes you in some way better than everyone else in the room? Keep that in mind, but don't tell your date about why you rock and others suck.
If a girl you have recently met is sitting there and telling you her feelings, she already only sees you as a friend. Sometimes dating, sex and a good relationships comes from that, but the majority of the time it does not.
The difference between how a romantic relationship and a friendship starts are completely different. The former starts out with some level of interest that is probably only based on attraction. The best way to attract a girl is to be confident in who you are and the things you say and do. With a truly confident person, a mistake comes off as a cute little error. With a neurotic mess who is not confident, it seems like an earth shattering error that there is not coming back from. It's displayed in verbal and body language.
In the latter starts out with no attraction. Nice guys are often willing to listen and even put the other person before themselves, but the initially reason for contact is not based on attraction, but a need to fill an emotional void.
This is important, when a girl is attracted to you, the void doesn't exist till you are not there, if a girl is not attracted to you, the void exists and you are the first person to come along and fill it.
That is my two cents. Flame away.