It's always exhilarating to see actors who've been stuck in one-dimensional roles get an opportunity to strut their stuff. Never has this been truer than in the case of Alexander, who went from peripheral parts in NBC's NewsRadio and ER to a magnificently multifaceted performance as Fran Boyd, a smack-addicted Baltimore mom who ultimately kicks her habit, in HBO's Emmy-winning miniseries The Corner. ''I understood the woman in a very private place that didn't have much to do with acting I knew her at a gut level,'' says Alexander. ''I felt I could bring dignity to her.'' She brought that and much more. ''All those terrible-looking wigs were mine,'' the 42-year-old actress proudly reports. ''I love playing characters that are unrecognizable.'' After her work on The Corner, Alexander no longer has to worry about her talents going unrecognized.