BGInfo is for displaying a background image on the desktop. It cannot be dynamically updated. What happens is that BGInfo loads the data you want to show and creates a bitmap. Then it merges the bitmap into your current background (or uses a static background depending upon your settings). Hence it is not dynamic and without taking a perf hit you aren't going to be able to keep it up to date. To be honest Task Manager and/or Process Explorer can show this same information in the sys tray so I don't see why you would need to do that anyway.
The same goes for disk space and info as far as BGInfo goes. You can do it via a WMI query but it is not going to be kept up to date. It'll run the query at startup (I believe) and then be static from there. Nevertheless you can use WMI to get the data you need but you'll need to create a separate query for each drive so, again, not automatic.