Hi,
If you work hard at optimizing and getting the directory to list good sites, google will recognize the resource and it will come up in a search for the terms you are focusing on.
With the current algorithm, Google tends to give well designed and populated directories a good page rank and good placement... so there is hope for your directory.
Try not to do the "based on DMOZ" results you see all over the Net. Less work and planning - even online - results in a bad user experience and a site that won't get off the ground. Try adding some good articles on the subject. Get a news feed that zeros in on your topic. The more resources you provide, the better your directory will be and the more it will get used.
We've been working on the Chiff directory day and night for months and have gotten decent placement and page rank... but we pay for it with loss of sleep and social life ;-)
Starting a business - that's what your directory is - takes focus and time. If you're willing to put the effort in, it gets noticed by your users and the search engines - including Google - will pick up on it.
mchiff
http://www.chiff.com