wireless access point

hello! 🙂 the situation is, i’m planning to put more than 1 access points and connect them to a switch. 1 have 3 questions:

1) If the signal from access point(s) overlaps, how will a nic decide which one to choose?

2) For indoor environment, how is the performance of 802.11b in terms of data rate and range?

3) will there be any noticable difference if i installed a high gain antenna? and if there is, will it worth the cost?

pardon me for this newbie question 🙂 thanks in advance 🙂