ZoneAlarm has no compatibility problems with BitDefender. I use ZoneAlarm Security Suite and BitDefender 9 Professional Plus on my system. I have enabled all the features in both of them (i.e. I have two firewalls, antiviruses, antispywares and antispams) and they never conflict with each other. I know it is not recommended but I decided to give it a go on a whim and apart from a few extra notifications (a program has to be allowed for internet excess twice the first time it tries to do so), I haven't had any problems at all.
