>The GUI will need to be pretty rich. The web app will be pretty hefty, as will the information that we need to push across it and persist between posts.
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>Right now, our strategy will probably be to pull all the data the client is likely to need for the DB but use DHTML to only display what they need to see so that the user can navigate through tree structures to see the info that they need. Any real processing will happen server-side. We want to push as much validation onto the client as we can and, as much as possible, handle all hide/show display issues there.

Validation on the client side will require heavy using of JScripts. If the apps will intranet and they will use it at regulary basis caching on the client PC will reduce the trafic.

>I have been looking at Client Callbacks, which are coming in ASP.NET 2.0. There is a nice introduction at http://fredrik.nsquared2.com/viewpost.aspx?PostID=113 that clearly walks through the simple sample code. I don't think that we will want to consider remote scripting. The only possible advantage to using remote scripting would seem to be broader browser support.
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>I don't think that we would want to do a browser plug-in because of the problems with code maintenance. We have complex business rules that change pretty frequently and making end-users download a lot of plug-in updates would undermine a lot of the benefits of a web app.

I didn't advice you too, but it depend. In our case precise printing force us to create plug-in

>I should probably research the validation controls available for ASP.NET. I have a VS.NET 2.0 beta 2 DVD. I just need to explore it at home so it won't cause problems for my copy of VS.NET 1.1 at work.

For your regret there is not so much controls for newest ASP2.0, in diffrence for ASP1.1. May be if you like to use ready controls you will have to wait at least an year for start of the development. Now we are making ASP2.0 Beta 2 application for utility company and most of the controls we are creating alone. We thougth that it will be easy to port our old ASP1.1 controls in ASP2.0, but this expectations appears to be wrong.