[kh99]

I think the problem is that $totalonline isn't registered to the header template, and also it might not have been calculated at the time that the header template is rendered. You'd probably need to make a plugin (using hook parse_template) with code that calculates $totalonline and preRegisters the value to the header template.

If you could live with the value only being dispalyed on pages that calculate it, then you might be able to do some sort of str_replace() on the $header variable before it's used in the page template (but that's a little trickier).