I get the following error when running my Visual Studio 2008 ASP.NET project (start without Debugging) on my XP Professional box:
System.Web.HttpException: T
Either grant that user the level of access to that directory, or change the identity that the application's application pool runs under - in IIS Manager, determine what App Pool is used to run your application, then in the App Pool section of IIS Manager, look at the properties for that pool - the tab you want is "Identity" I think (this is off the top of my head).
You can set it to another user account - for example, Crystal Reports .Net requires update and delete access to C:\Temp - so we have a "webmaster" user, with administrator access, and use that identity for those applications.