Here is a good page on using meta tags like “description” and “keywords”, and how they influence (or rather: don’t influence) search engine rankings.
Remember, you are using these tags to help make up for the lack of text on your pages, not as a way to successfully anticipate every keyword variation a person might enter into a search engine. The only hope you have of ever doing that is to have good, descriptive pages with good titles and text that is not buried on the bottom of the page by JavaScript, frames tags or tables. The meta tags are a tool to get around these aforementioned problems.