Wireless network: I can't have internet and Network between computers?

I've just set up my house with a wireless network. The
internet works on all computers, but when (i have windows
xp by the way) i clicked the option of creating a home
office network between the computers to share files and
use one printer, but then it screwed up my internet
connection. It has something to do with the IP
configuration i think. Could you help me have internet on
all computers, but still be able to use one printer and
transfer files easily?
Thanks,
Mark

Oh also, for wireless, do all computers have to be on to
have connection and not just the modem and router?