Think about the wireless card like a regular NIC and an access point like a Hub.
Yes you can connect two computers without a hub (using a crossover cable) and yes you can connect two computers without an access point (using adhoc mode instead of infrastructure)
I would highly recommend paying the extra money (as little as $25 extra) to get a access point as it is much easier to use and will likely give you a longer range since the antenna is better on the access points.
Just like there a routers and other multipurpose devices (Firewall/NAT/DHCP/etc.) with built in hubs, these same devices can be purchased with a built in access point. Determine your overall need to decide what to purchase. If you are considering just two NICS then I would recommend the DWL-1000ap for $195 at buy.com - http://www.us.buy.com/retail/product.asp?sku=10258307&loc=101
Get an additional $10 off
The PCI version of the NIC is $165 so as you can see the access point is really not much more.