this is actually the query im using presently

new Wordpress_Query("cat=&showposts=20&offset=$offset")

What I have to do is obtain the final amount of posts in order to setup some kind of pagination function. Offseting because the person chooses the following posts.

you should use wordpress_count_posts - see http://codex.wordpress.org/Function_Reference/wp_count_posts

You cannot obtain the final amount of posts using wordpress_query , but you should use $wpdb class to locate it .

Makes sound practice to try and build you are own pluggin consider you will find a lot of them available ... WP-Paginate .

And the other sound practice is always to set the amount of posts per page from wordpress-admin , and never hardcoded in you are theme .