Hi there,
Depends on what you mean by directory structure. The layout you have is very crisp and clean. To grab really good keywords try, google's traffic estimate or yahoo search marketing to find keywords. Wordtracker is good if you are willing to pay for keywords, as was already suggested,
The key to ranking for keywords is :-
meta tags - title, meta keyword, meta description
h1 and h2 tags with your keywords there
first sentence and sparringly throughout your page you should place keywords again as was mentioned before remmember you are writing this for human eyes not google crawlers
bold text
same site url's - the links to your internal pages, make sure some of the anchor text, contains the keywords
outbound url's - depending on how many sites you link too...put some no follow tags on to preserve link juice
image alt's - make sure you images have keywords in them (sparringly)
hope this helps