Drupal 6.x

I would like to override the default theme logo or replace it with an image. I think it could be done via CSS.
Can someone please send me a sample code that I can use to do this?
example:
I want to insert an image at the top left corner of the screen, it will overlap the menu bar (brought to front of everything), making it look like a 3D image.

I'm trying to implement a method to see which employee is in the office and who is out with a single glance.

Users (or employees) need to click a button to show they are in and click it again to show they are out (toggle).

Which module(s) can I use to implement something like this? Or how can I implement something like this that would need minimal interaction from the user.

Any help would be appreciated.

I have a couple of D6 and one D7 sites which have been targeted by spammers who have created accounts. I switched quite a while back to requiring a user to contact me after creating the account before it could be activated, but that didn't keep a lot of fake users from being created (over 7800 in the D7 site and it barely exists). If we ever finish the D7 site, we will want users, so I would be interested in hearing about good ways to manage that without getting this kind of garbage, but in the meantime I am wondering if there is an easy way to clean up these unwanted users.

I have had someone report a spam e-mail which appeared to originate from my Drupal website hosted by Westhost. I can see, in fact, that it has been blacklisted by some sites. At the site, I can see a large number of inbound e-mails which are all reports of failed e-mails being sent, e.g., like a spam bot was sending from a list that was not up to date. These add up very quickly. There are also a smaller number in the outbound mail queue. Perhaps those are from unreachable systems.

Westhost suggested that changing the password of my login might fix things. It didn't.

Hey there :) Happy new year and Merry Christmas everybody.

I had a working test site of Drupal 6 that I just have upgraded from 5 with your kind documentation in this great community. I am faithful advocate of Drupal but am no developer and with mediocre access to my hosting place.

As it is obvious that D6 support is already dying I am now forced to start the process of migrating all my sites to D7.

I have been looking for some kind of tutorial that will help migrate complex large sites and the best I have found is this one http://d6to7.drupalgardens.com/content/modules-and-upgrade-paths
but it doesn't seem to have been updated for a while.