Linux and Windows Soft AP

Windows 7
To create a SSID for soft AP, execute following command as administrator

netsh wlan set hostednetwork mode=allow ssid=yourssid key=yoursecretkey

To start soft AP

netsh wlan start hostednetwork

PS: You need to share "wired connection" (Local Area Connection) for your clients.

Linux
To install hostapd

yum install hostapd

To modify hostapd configuration

vi /etc/hostapd/hostapd.conf

#WPA (1: WEP, 2:WPA, 3:WEP + WPA)
wpa=2
#Secret key
wpa_passphrase=yoursecretkey
#Wireless interface
interface=wlan0
#Support wireless mode(use b for better compatibility)
hw_mode=g
#Wireless channel
channel=1
#SSID
ssid=yourssid

PS: You need to prepare dhcpd and nat (iptables) for your clients.