This post include 2 part. In first one I’ll describe step which should be taken on linux machine and in second one step for windows client.

Linux(server side)

We use this host to share internet connection between users over wireless network, so the machine has to have at least two connection:

1. Internet ( regular ethernet connection)
2. Wireless connection( provided by wi-fi card)

I will skip how to setup your Internet connection, therefore make sure its work properly.
If you mounted your wi-fi card to pci slot use lspci to check it out:

[root@localhost ~]# lspci  | grep -i wireless
02:01.0 Ethernet controller: Atheros Communications Inc. Atheros AR5001X+ Wireless Network Adapter (rev 01)

For this card kernel module ath5k should be loaded into the kernel. Check it:

lsmod | grep ath5k

Use modprobe unless module is not loaded.

modprobe ath5k

If you done it without any problem I will able to set up the wi-fi card. Here is network configuration file for interface wlan0 with some comments:

[root@localhost ~]# cat /etc/sysconfig/network-scripts/ifcfg-wlan0# Atheros Communications Inc. Atheros AR5001X+ Wireless Network Adapter
DEVICE=wlan0
ONBOOT=yes
IPADDR=192.168.0.1
NETMASK=255.255.255.0
HWADDR=00:17:9a:b7:d6:01
TYPE=Wireless
MODE=Ad-Hoc  # set this mode if want to make this card as access point
ESSID=homeee # the name of this connection which will be displayed for users
KEY=dffb9e2cc2 # secret key for connection

To generate connection key run:

dd if=/dev/random bs=1 count=5| xxd -ps

Now restart the network service:

service network restart

and verify:

iwconfig wlan0

and

ifconfig wlan0

So 50% of linux part is done. Tune your kernel to make it forward ip traffic:

vi /etc/sysctl.conf

and set

net.ipv4.ip_forward

to 1:
net.ipv4.ip_forward = 1
Make changes affected:

sysctl -p /etc/sysctl.conf

Verify:

sysctl -a | grep all.forwarding | grep ipv4

And last but very important step. Its firewall and nat settings:
!!! Be careful because this command flush all your rules in OUTPUT chain

iptables -F OUTPUT

turn masquerading on:

 iptables -t nat -I POSTROUTING -s 192.168.0.2/32 -o eth0 -j MASQUERADE

where eth0 your interface for share.
save it all:

service iptables save

The linux router is ready on all 100%.

Windows(client side)

I use windows Vista for this, but this steps can be used to Windows XP as well. Go to:
Start->Control Panel->Network and Internet-> Network and Sharing center -> manage network connections
Click right button on your Wireless Network Connection and choose Properties.
Make double click on Internet Protocol Version 4.
When new window is appear fill it up:
Ip address: 192.168.0.2
Subnet mask: 255.255.255.0
Default gateway: 192.168.0.1
Also you need to specify you DNS server. Put the ip address of DNS server provided by your ISP.