I'm not sure if it can be done at install time, but it's very easy after you're booted up. Almost all cards I've tried are supported by the basic drivers, and enabling third-party driver support (to get nvidia drivers, etc straight from the commercial source) is as simple as System->Administration->Additional Drivers. Click activate and you're good to go.
I admit ignorance--the last time I used Ubuntu regularly on the desktop was just before my first mac arrived in late 2006. I've toyed with it since then; but never gone through installation and configuration.