When you use VS 2008 to open an existing ASP.NET 2.0
application that uses ASP.NET AJAX 1.0, you can alternatively choose not to
upgrade it to .NET 3.5, and instead use the new multi-targeting features of VS
2008 to build it using ASP.NET 2.0 and ASP.NET AJAX 1.0.
The VS Web Tools team recently published a Using VS 2008 to Target ASP.NET AJAX 1.0 blog post that
describes the step-by-step instructions to accomplish this using VS 2008
Included in the blog post are a number of manual steps you
need to take in Beta2 to populate the VS 2008 toolbox with ASP.NET AJAX
1.0 and ASP.NET AJAX Control Toolkit server controls. For the final
release of VS 2008 we'll release a setup package that will automate this for
you, as well as add ASP.NET AJAX 1.0 project and item templates to VS 2008
for you to use.
You might be wondering - why is it interesting to target
ASP.NET AJAX 1.0 applications using VS 2008 instead of just using VS
2005? The benefit is that it enables you to build ASP.NET AJAX 1.0
applications that work on your existing servers (no need to upgrade them to
.NET 3.5 immediately), while still allowing you to take advantage of some of
integration support with TFS, and more.