Is it posible to change to a new layout when a person select a value in a value list ? I need to hide some field that they dont need to fill in if they dont select just a special field in they value list?

There are a couple of tricks and techniques that you could consider using to solve your current problem.

One would be the script triggering method that uses a pop-up list, then runs a script according to what value is selected (in your case the script would decide whether or not to change layouts depending on the value the user chooses).

A couple of files produced by Al Fleming and James Mastrianni which demonstrate variations on this technique are in a zip bundle on my server, and you'd be welcome to download them and take a look. Their demos are unlocked so you can pull them apart to see how they work. Th zip archive with both demo files in it is at:

http://www.nightwing.com.au/FileMaker/script_trigger.zip

Another, rather different approach that would perhaps get you the effect you want is one based on the widely used 'visibility' technique. This is an effect where layout objects such as fields remain invisible unless a particular value is entered into a field, whereupon they appear. There are many uses of it, but one would be for the kind of situation you've described.

A demo file that shows an application of the technique which is more or less along the lines you're looking has been produced and published by J M Osbourne of the www.databasepros.com site. I've located a copy of that one and put it on my server too if you're interested. It is at:

http://www.nightwing.com.au/FileMaker/Visibility.ZIP

Thanks Cobaltsky that solved my problem i have now 5 hidden objects that will be visible it the user select right value in my value list

Thousands thanks for the fast answer and the nice solution !