Dotnet framework 3.5 is built upon the framework 2.0 so all the features are supported that were supported on the asp.net 2.0 with some additional features added.

Features of asp.net 3.5

Integrated Asp.net Ajax toolkit.

Integrated ASP.NET Ajax toolkit, which provide developers with much better tools for creating highly responsive web pages, along with impressive effects like we see in our desktop applications. Asp.net ajax toolkit comes along with asp.net 3.5. For asp.net 2.0 we have to seperately install the ajax toolkit.

Linq

Most awaited feature of dotnet framework 3.5 is Linq which allows developers to easilty create data access layer. Its more like ORM feature for dotnetframework 3.5.

WCF

Developers can use WCF (Windows comunication foundation) instead of web services for more managable and robust web applications. Make easier communication with the server from the browser for more interactive web applications.