Help! Black tie event - what the hell to wear????

[juneau]

I haven't been to a black tie event since I was, oh, 20-something? I own nothing even remotely posh frock-ish and for one night I'm thinking I'll probably rent. But what? What the hell do you wear nowadays? The kind of 'ball dress' I wore 15 years ago is not going to suit me any more. I'm 38, 5'4", slim, but hourglass shaped. Any ideas?

Something like this?

www.coast-stores.com/SAVANNAH-MAXI-DRESS/Maxi-Dresses/coast/fcp-product/2224752380

Given that there are maxi dresses everywhere and Christmas is coming, I would have thought there'd be lots of options. I think long, but not bridesmaidy is the answer.