With the latest upgrade to iOS 5.1, Apple TV can indeed connect to WPA2 Enterprise encryption. You'll need to configure a profile using Apple configurator that includes the certificate chain for the connection and the connection information.
See http://support.apple.com/kb/HT5438 for 802.1x connectivity for Apple TV with iOS 5.1
There appears to be a small hiccup (bug) that others haver reported. I can't verify that IS what I've run up against and haven't had time to test the 1st deployment for this bug. It appears that the aTv gets it's time from an ntp server. Without that connection, the default date is set to sometime in 1969. With this invalid date, the Apple TV thinks your certificates are invalid and will not connect. This only occurrs if the device has lost power / unplugged. The apparent ugly solution as suggested by another on these forums is that if it loses power (hence the time), to plug in an ethernet connection until it can reset the time. With the correct date, the unit will connect into the WPA2 Enterprise Wifi. I was having a bugger of a time trying to figure out what was going on with the programming that we did in another room and then move the unit into the classroom and it would lose it's connection. Following the ethernet suggestion, (left it in for 5 minutes) the device connected up via wifi - no issues.
PS - APPLE - if this is indeed a bug, fix it please.
I also have this problem and would appreciate a solution, rather than a direction to elsewhere. The apple tv screen says to come to apple support for help and there is none available. It is indeed a bug and it needs fixing because it would be very easy to connect to a network that the Ipad itself can connect to.