you should get something with minimum 802.11g
Also we need more specifics about what you want these two computer so do, like connect to the internet and what internet connection you have. But as how I would set it up if I were in your shoes, I would get get:
2x 802.11g PCI cards (either from Netgear or D-Link) $67.65 for the DWL-G520+
1x 802.11g Wireless Access Point (Netgear or D-Link) $121.45 for the DWL-2000AP+
with these prices your looking at around $250
prices are taken from techbuy.com.au
If you have broadband Internet and have a router, get a wireless router or then again you could just connect the WAP (Wireless Access Point) to the router and make it point to the router.