i have a domain with 3 character. it's pr is 3 now, not fake pr. it have good link back from yahoo/google. is it will be a good directory?
What's the name of the domain? Its hard to tell you anything if we don't know more info. Anyway you should be able to have a successful directory with any domain name.
Domain is not the only factor which makes directory popular, there are many thing besides this which you need to focus on.
The best way to make the directory is to start it from scratch well this also include the domain name registration.
One of the most important factor for successful directory is maintenance and regular updates, may require lots of human hours.