[OS X TeX] Questions on MacTex installation

[Christoph Hoh]

Dear list members,

I have been using Tex on my Mac for a while now. I downloaded the  
MacTeX-2007 package in July 2007 from the MacTeX site.
Today I checked the website again and found out that there are  
different other downloads available.

After reading most of the explanations regarding available downloads,  
several things are still not clear to me:

1) What is the difference between the MacTeX-Additions (126.1 MB) and  
the MacTeXtras (280 MB) - except the file size?
    Is all the software of the MacTeX-Additions included in the  
MacTeXtras? Is all the software of the Additions and Extras included  
in the MacTeX-2007 package?

2) The actual MacTeX package on CTAN (http://ctan.tug.org/tex-archive/ 
systems/mac/mactex/) is dated with 2007-12-01. Since I installed the  
MacTeX package in July 2007, I would like to update the package. How  
can I easily upgrade to the actual version without uninstalling my  
own installation?

3) In case that there will be a MacTeX-2008 package in near future,  
will I have to uninstall the MacteX-2007 installation prior to  
install the 2008 package?

Thank you for your help in advance!

Regards,
Christoph