Solaris

I am learning Solaris Zones and I have the following doubts:

1.Sun has developed both Zones concept as well as Virtual Box concept. To work in Solaris if zones method is there, what is the need for virtual box?
From my little knowledge, I feel virtual box and the whole root zone are same except virtual box is gui oriented. please correct if wrong.

2.I am aware that sparse root zone just shares filesystems from the global zone and if the shared files are deleted from the global zone it affects the sparse root zone too.. please let me know in what situation a sparse root will be used and in what situation does a whole root zone be used?

Many thanks to you all ....

1:
They are not at all the same. VirtualBox is virtualizing an x86 PC while a Solaris zone is virtualizing the Operating System. They work at a different layer. Zones are faster, run on any Solaris 10 hardware but cannot run but Solaris or Linux. VirtualBox doesn't run on SPARCs but run almost any OS that can be installed on a PC.
2:
The main reason sparse zones are used is to save disk space and time.

jlliagre.. thanks for clearing my doubt. Some more doubts....
1.Is it possible to have zones in GUI environment?
2.Suppose if I am having an x86 machine installed with Solaris , which opttion is better? Virtualbox or Zones?
My problem is i am not aware of the " difference between virtualizing a x86 pc and viirtualizing an operating system.. "sorry for that..
thanks

1: You can display a desktop or any graphic application from a zone.
2: "both" are better dependings on the needs. You do not tell what you want to do with them.
Virtualizing hardware means you can install windows, *bsd and more exotic OSes.
Virtualizing the OS means there is a single OS instance running for both the "host" and the "guest".

jlliagre,..thanks..