I want to put a table in my content bar, but in some screens the table is over the right sidebar. I use a simple table, copied from word, no photos or anything else included.

you should never copy anything from a word document and paste it into a post. Word has embedded code that messes things up.

there is a 'paste from Word' icon in the post editor you should use to strip the embedded code.

This is what I mean, that I copy it with the special button.

What is the url

http://potohori.gr/2012/09/09/test/ this is the link when I have a simple table.
http://potohori.gr/2013/02/20/poll3a/ this is the link when I put the table in Contact Form 7 (this is what really interests me now.
When I use my laptop wchich has a good screen 15'6 chrome or IE everything is ok. With older pc's though there are problems. Probably I have to put a code that resizes the table.

you need to remove all the embeded styling in the table. For example change

<td valign="bottom" nowrap="nowrap" width="261"><b>ΥΠΟΨΗΨΙΕΣ</b></td>

to

<td><b>ΥΠΟΨΗΨΙΕΣ</b></td>