Unless you got multiple IP addresses from your wireless provider, use NAT and enable forwarding. Change ppp0 to the interface with your net connection if different:
Code:
/sbin/modprobe iptable_nat
/sbin/iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
echo 1 > /proc/sys/net/ipv4/ip_forward
You'll need to manually enter DNS server details in Windows for name resolution.