Customizable Interface within a Webpage - how? (Similar to http://my.av.com/ )

I am opening a website, and I'd like to configure it so that users can choose what is displayed on the page they're viewing - and have their configurations saved the next time they come to the site. A good example is with Altavista's "My Altavista" feature. View here: http://my.av.com/

At Altavista's page one can choose from a series of options: local weather, horoscopes based on your zodiac sign, lottery number drawings, and a string of other variables that pop up on the screen. These are all configured solely by the person viewing the web page, and each time the person accesses the site again - his information is displayed.

It makes for a great resource.

I'm sure this is a huge undertaking, and so before I ask for an in-depth explanation from somebody, maybe just a brief one. What do I need on the server-side? What does the client need? How complicated is this, and how knowledgable must I be?

Thanks for your time, anyone who reads/replies to this.

Sincerely,

Mannequin
manequinn1@yahoo.com