That second part makes it seem like it may be a mini-kies update which would mean that it wouldn’t be available to Mac users, so Mac users find a friend with a PC. Also, AT&T core stores usually don’t do this for you but there are dealer stores out there that can put the update on your phone, just look for them.
In the video interview with AT&T’s Android lead Dante Martin, he doesn’t cover the Samsung Captivate update but he does say that the HTC Aria he has in his pocket has Froyo on it and that Froyo would be available to the masses soon.
And here’s that video:
Source: AT&T Facebook