You would probably need to use a mix of the codes html,php and javascript. or you could try using asp with ajax
References :

ABSOLUTELY NO WYSIWYG whatsoever!
At the minimum, you need to code using (X)HTML, javascript, php, mySQL, AJAX, on a LAMP server, (more on a window server), and develop your code using a plain text editor like Notepad++.
Any attempt with Dreamweaver, Frontpage or other IDE will lamentably fail.
Web design IDEs are made for amateurs to make statics sites, nothing else.
You have a very long way to go, so, start coding!
Good luck!
References :

hello,have you heard of drupal content management systems?It is a powerful open source software and so dynamic.Its limit is what you are not thinking of.I personally run a drupal content management system and the site was designed by Drupal consultants and Pathfinder consultants.The guys are very affordable and very savvy as well
References :
Drupal Consultants and Pathfinder developers at http://www.pound-investors.com

You can design such kind of web site by using asp.nte, php, dupal.
This kind of software are use for web development like igoogle and my yahoo sites. you can make contact us through Letsnurture
References :

It is a real hard thing to say being those examples are fully developed applications for the most part. To build the base yourself you would have to look into a web development language like Ruby, PHP, ASP, or etc. I would recommend PHP or Ruby for the open source community behind them. Then using a framework and MVC pattern to structure your code and make things easier. (i.e. Rails or Zend)

Now their are a few open source platforms created already you can install, but none offer the complete solution really. If you want basic functionality and something easy to use I would look into the PHP solution of Wordpress, Drupal, or CMS Made Simple. You can customize these to do what you want with less code and maybe some prebuilt plugins but they will not be as clean or nice as building your own.

Then lastly when it comes down to designing your modules and pages you should look at just using your typical design software from Adobe or the open source programs GIMP or so forth. Just plan out what you want your application to do before you being and keep that in mind while actually designing the modules. If you lose sight of the end scope you could box yourself in with a design that does not function modularly.

Sorry for possibly stating things that were not needed but I wanted to cover most bases in case the information was not known.

EDIT: I forgot to add the information about the Front-End Interface. Both those sites use what is called AJAX, which is basically using JavaScript to reload and send data to code in the back end to return results to the front page so that the user never has to leave his current page, if you google this you will find many resources and there are even a couple frameworks for this like JQuery and MooTools.
References :
Professional Web Designer/Developer
http://www.cmsmadesimple.org
http://www.drupal.org
http://www.wordpress.org

http://en.wikipedia.org/wiki/Model-view-controller
http://www.rubyonrails.org/
http://framework.zend.com/