Both your PC will need a piece of hardware called a "wireless adapter card". They occupy a PCI slot if you wish to install them internally within your PC or you can get the USB wireless cards which simply utilizes the USB port.
LINKSYS WMP54G IEEE 802.11b/g PCI Wireless Adapter up to 54Mbps Data Rates 64/128-Bit WEP
You need an access point for internet connection/network connection and for that, you will need a wireless router.
LINKSYS WRT54G IEEE 802.11b/g, 802.3 Wireless-G Broadband Router
Are you using broadband internet such as DSL or cable?
After all that is installed, you will need to enable Microsoft's File and Print Sharing within Windows on each PC to initate network share. By doing this, you will achieve internet sharing and home networking wirelessly.