You can sign up for an AOL account (they're free now), start up the AOL software (the old all-in-one style), open the .ART file, and take a screen shot.
EDIT: It looks like the AOL software will let you open and display .art files without signing in, just tell it to ignore the sign-up stuff the first time you run it.
EDIT again: just adding some more details in case anyone else runs into these nasty little files:
If the AOL client isn't already preloaded in your Mac's applications folder, get it from
http://downloads.channel.aol.com/macproducts Go ahead and use the "Easy install" option, it's not like the old Windows versions that used to screw up networking.
When the client starts up, you can press the Cancel button at the first-run Welcome dialog, if you don't have or want an account.
You'll now see the login screen, ignore it.
Pick File->Open… from the menu, find your .ART file, and do the dirty deed.