It used to be that this trick worked quite well. The problem is that this has not worked for more than 2 years now. Everybody and their cousin began using this practice, causing search results to be totally irrelevant. The odds are good that it will get you banned from the search engine altogether. Do not use it.
Meta tags are only a small part of the ranking systems.
And that is only on some search engines. Many do not use them at all for relevancy. Yahoo, Excite, Webcrawler, and the Open Directory Project don't care a whit about your keyword meta tags. To varying degrees, search engines also take into account your site's title, headings, domain name, file names, and the text of the site itself. Additionally, many sites which rank high do so because of their hard work.