Display Member Count and Currently Active Users in Welcome Message or Notice

I remember DaniWeb used to show currently active users and also total member count in the header (above the forums).

I've been told on vB forums that its not an easy thing to do. I wish to know how to display the information in header/guest notice etc.

The best way would be to look at the query and put it on a global hook. Then you should be able to use the varables set in any template.