Installing Drupal

Well, it exists for me, but not for Drupal. In the 'settings' page I get this red message:

The directory /tmp does not exist.

And, at the top of the page:

warning: mkdir(): SAFE MODE Restriction in effect. The script whose uid/gid is 1761/48 is not allowed to access / owned by uid/gid 0/0 in /var/www/xx/xx/drupal/includes/file.inc on line 78.

I add the following code to Home->administer->themes->global settings->global settings:

<a href="/?" class="home">Home</a>
<a href="/?q=contact" class="contact">contact</a>

I have 2 problem:
1. It's nothing after I click "contact" menu item.
2. I want to let menu item look nicer,e.g:colored border,or bitmap background.

Please help me,and thanks.

I want to add profix for all tables,e.g:dr_
How do I do?
Thanks.

When I go localy to http://localhost/drupal everythng works perfect
but when I try to reach drupal from an other computer on the network

I also can brows it but the collors and pictures are not showing at all..

Anybody some advice???

Regards
T.

I want to use use oscommerce system to create a online shop,and it run well.
I want to use drupal system to give more detail for product now,but I find a same table name between drupal and oscommerce,and it is 'sessions'.
How do I kill the problem?
Thanks.

update by bertboerland: fixed the links, please use propper HTML instead of brackets. And use http:// for the websites.

I want to use use [url=www.oscommerce.com]oscommerce system[/url] to create a online shop,and it run well.
I want to use [url=www.drupal.org]drupal system[/url] to give more detail for product now,but I find a same table name between drupal and oscommerce,and it is 'sessions'.
How do I kill the problem?
Thanks.