Post installation

I'm running a few Drupal sites and planning more.
All sites are completely separate, but maintenance would be much simpler if there was just one codebase. Despite hours of reading, I just don't get how to make it work. I'd happily write it up for other users if someone can help. Here is the position:

Drupal is installed in the root of www.examplesite.com, and there is a subdomain newsite/examplesite.com. Each has its own database.

What does "robots.txt not found" mean?

Its a frequent "page not found" entry in my log.

Any ideas would be very helpful.

Thank you

How to display a Menu/block "User login" without the two items "Create new account" and "Request new password" ? I want to see only the two blank fields "Username" and "Password".
It seems it's not a basic Drupal setting (I'm a newbie).
I ask this question because I plan to administrate my site with pre-registered users / passwords.
Thanks in advance for your help.

When I create a menu item to something like my FAQ and place it in a menu item linked to 'node/28' it works fine from any section such as administration, or 'my blog'..

however when I create a block in which i have the following:
<a href="node/13">ad info</a>

it does not work properly on some pages such as administration or 'my blog'.. it appends the 'node/13' to the end of the current URL (as is expected)..

I just installed the Wiki module on our Drupal installation, but it is not doing what it is supposed to do. Let me explain what I did and what the results are:

I'm looking for a module that allows voting. I need to have a page or whatever a module uses be promoted to the front page after either a certain amount of votes or after having the highest amount of votes of all pages and then a certain amount is promoted to the front page. As with digg, I'd like things to degrade and go after a certain period even if it has the most votes/diggs. I'd also like a karma system where a user gets karma/points for creating a post and karma/points for voting.