I am using the Flash detection pluggin in DW. The problem is that the pluggin
just check if the visitor has Flash installed and not the flashplayer version
itself. Is there a pluggin to add for this to DW or is there some other easy
way to fix this problem?

Try this page:
http://www.adobe.com/devnet/flash/articles/swfobject_print.html

Thx mate. However i am not the code type of guy :( I really have difficulties
to understand how to implement these codestrings. Could sb please explain which
lines i should put in the first frame in my movie and which lines in the html
doc? I am really confused about this.

I also am not a code guy, but was able to learn enough to get my first page
working by using the original SWFObject blog page here:
http://blog.deconcept.com/swfobject/.

As with any code-based feature, there are a number of options that are
explained and at first it is not clear when you need some of these options.
So, unless you are into some more advanced stuff than simply playing a Flash
movie in a web page all the options discussions can muddy the picture.

In the simplest implementation, you do not need any AS code added to the
movie. Just add the swobject.js file to the root directory of the web site and
use a simple HTML snippet as shown in the above referenced page section titled
"How it Works".

If you are using DW, here is a link to a DW extension that will create the
HTML stuff for you http://www.communitymx.com/abstract.cfm?cid=3DA1E.

Here is a free SWFObject Extension that you can add to Flash authoring
application that will allow you to select an HTML Template (Publish Settings)
and it will create the HTML for you:
http://flog.fluid.com/experiments/swfobject-extension/

The references to adding AS code to the movie refer to a very nice feature
called "Express Install". This allows the install/update of Flash Player
without having to leave your web page.

When you download the ZIP file from the article link, you get a sample HTML
and sample FLA that show how to set up the HTML and the Express Install option.

Hope this helps a bit.