re:
!> I'm running XP Pro/SP2
!> I do NOT want to use the built-in Cassini Web server and instead want to use IIS6

You can't. You must use IIS 5.1, which is XP's IIS version.
IIS 6 can only be used in Windows 2003 Server.

re:
!> How do I make VS 2008 use IIS for my project rather than the "built-in" (cassini) Web server?
!> I ran into trouble when I selected "IIS Web server" in the project properties (Web tab).

You'd first have to create an IIS virtual directory for your application.

Then, in the project's Property Pages dialog box, click the Start Options tab.

Under Server, click Use custom server
...and write in the full path to the IIS virtual directory in the "Base URL" textbox.

Juan T. Llibre, asp.net MVP
asp.net faq : http://asp.net.do/faq/
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Cassini? Have not heard that name in a while, but you are correct. That is
where it got its start. Officially, it is now the ASP.NET Development
Server.

Change the drop down to HTTP and specify the URL. This will be your new
default. This happens when you create the site.

How to change from file to IIS (ASP.NET Dev Server to IIS):
1. Find the folder in question
2. Right click and choose web sharing
3. Make sure Execute Scripts is selected
4. Close web in VS
5. Choose Open Web and then make sure you are opening off IIS

NOTE: If you have IIS set to default, open the IIS Manager and ensure
anonymous access is selected. It will be unchecked if you have not altered
your default set up. If authentication is not set up correctly, it can
interfere with debugging.

Most likely wrong version of .NET as default (see below).

Run aspnet_regiis -i from the 2.0 folder again. That should get everything
registered correctly for you. There is a tool for quick switching between
ASP.NET Framework versions. You can check this fairly easily by opening the
IIS manager and viewing the mappings for .aspx, etc. If mapped to version
1.x, then running the aspnet_regiis -i will work.

NOTE: This will set all sites to the new version, not just the one. If the
majority of your local sites are 1.1, you might want to get the tool I have
mentioned:
http://www.denisbauer.com/NETTools/ASPNETVersionSwitcher.aspx

All the tool does is run aspnet_regiis -s {website} (which is the IIS {root}
name, not just a friendly MySite}

Make sure the config file is correct. That can cause it to bugger up. If you
start without debugging, you will see the error.

It can also be a problem with your solution file, although I think this is
resolved in 2.0 or later.

Make sure you have windows authentication set up in IIS. That will cause it
to not work.

Here is a link to KBs on this error message:
http://tinyurl.com/6a7jd9

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