Many posts

I have an installation of Wp 2.8.4 with 20.000+ posts.
SQL queries are getting slow, do you have any hints for optimization?

Looking at mysql slow queries log I see a lot of sql commands that are taking many seconds to execute, here a few ones:

SELECT SQL_CALC_FOUND_ROWS wp_sport_posts.* FROM wp_sport_posts WHERE 1=1 AND wp_sport_posts.post_type = ‘post’ AND (wp_sport_posts.post_status = ‘publish’) ORDER BY wp_sport_posts.post_date DESC LIMIT 0, 10;

SELECT SQL_CALC_FOUND_ROWS wp_sport_posts.* FROM wp_sport_posts WHERE 1=1 AND wp_sport_posts.post_type = ‘post’ AND (wp_sport_posts.post_status = ‘publish’) ORDER BY wp_sport_posts.ID ASC LIMIT 0, 1;