I would not use a .dwt template for a 50 page site. The template will (hopefully) update all 50 pages but by far the best way would be to investigate SSI (Server Side Includes).
The problem with .dwt template files is whilst they will update your pages you will also have to upload those 50 pages to your remote server every time you make a change to the template, tedious. If you use a SSI it means only uploading one file.
After having worked with .dwt files (which can be problematical) and SSI - I know which I prefer.
I second Osgood's sage advice. Server-side Includes are much better than DW Templates. Moreover, when a static site begins to exceed 50 pages, it's really time to start thinking dynamically -- server-side programming and SQL databases. In the long run, it will make site management much easier.
Thanks for your answers. I have tried to use SSI and it worked but I must make one file for the top menu bar and one bottom bar for contact information and insert them in the template SSI-file. I could not fix that in the same file; maybe I have done something wrong with the SSI template? In .dwt-file I can fix that in the same file and I can se the hole page in Dreamweaver when they are constructed.
You can have as many SSI files in a page as you like providing you have set everything up correctly so I don't know why you would be having issues.
I dont know what kind of SSI you are using but in php you would simply insert the two 'calls' to the include files in a page template where you need them.
<?php include('topMenu.php'); ?>
<?php include('contactInformation.php'); ?>