[support] multiple sites on one domain

[Roger]

I have a single user system and need to work on 2 quite different sites 
on my home pc before transferring them to the isp .

Where can I find instructions on how to set up and work on 2 quite 
separate web pages.
I guess they will use the same database so how would I separate each 
site so the components and database info can be transferred to a live 
ISP site.
At present I have separate drupal installations.

I believe there is a way to have one theme-set as the shop front - main 
page that everyone sees and another theme-set of pages for members. 
Where can I get instructions for beginners about this please.

Off subject--
Is it worth going over to Drupal 7 now instead of having to upgrade down 
the track.

TIA
Roger