Granted, there are more authoritative people with more in depth answers on this, but in short ... nope. ACL's are not Mac OS X's thing. OS X likes the simple unix permissions scheme. This is inherent in the 2 HD formats typically tossed around with OS X, HFS+ and UFS. ACL support should be coming eventually, though I don't know in what manner. Possibly a different HD format, possibly a sharing list only enforced through filesharing.
What is it that you need to do? In all reality, unix permissions can effectively do anything that I've seen ACL's do, but they aren't nearly as easy to modify when you decide to change things. ie, making one group a member of another group just doesn't happen on UFS. But you can certainly make all of the members of group members of another group too.
I'd also like to see an ACL list that the admin on the system can actually understand and explain. When people talk about security being difficult, they are usually referring to ACLs. I hope Apple re-engineers some of the ACL concepts before they put anything into production. NTFS is hell. I don't want to see that kind of pain on Mac OS X any time soon.
