As most IT Pros know, Wireless Encryption Protocol (WEP) as originally designed is not very secure. While better than nothing, it's not a great deal better and is easily cracked. In a great Cable Guy article, The Cable Guy (aka Joe Davies) explains WPA2 in the latest installment of his monthly TechNet column. A great introduction to WPA2. And there's an update to Windows XPSP2 to allow you to use WPA2.
I agree with the point Barry makes in the comments: you need up to date drivers for your network cards. Not all manufacturers are totally up to speed.