Two basic "How to" questions: cookie path and who's online
 

1. cookie path: how can I set up my cookie path so that someone logging on using www.xyz.com won't need to log in again when they click a link http://xyz.com (without the www) and vice versa.

2. i want the default listing on "currently active users/who's online" to be 50 users per page not 20 - how can I change that?

1. That is not cookie path, but cookie domain. Set the cookie domain to ".xyz.com".
2. Which page are you referring to exactly?

On the Main Index at the bottome there is a "What's Going On" section and in that a "currently active users" link - the default is 20 users per page when listing - I would like it to be 50 users per page (as default - I know it can be manually reset each time)

I think that is hard coded into the page. Go to includes/functions_online.php and look at the function sanitize_perpage and where it says "$default = 25". But that value is actually superseeded by 'maxthreads' in the call to it in online.php around line140. 'maxthreads' which is the "Maximum Displayed Threads Before Page Split". So, you can change that value in the vboptions or modify that line of code.