I would say the same thing that it should be in the bin folder, but if you
are correctly compiling the project and it isn't being put there, try double
checking these settings/properties:
1. In the Visual Studio .NET Solution Explorer, select the .cs file (or
whatever file you are compiling) and look at the Build Action property. This
should be set to Compile.
2. In the Visual Studio .NET Solution Explorer, right-click the project file
(I think it has the extension .csproj for C#, but the extension is not shown
in the Solution Explorer) and select Properties. Check the Common
Properties -> Reference Path property page. This page will list one
directory for each project in the current solution. These are the
directories where the .dll file(s) are saved, the directory is typically the
bin subdirectory of the folder that web.config and other files in the home
directory of the project are saved.
If these suggestions do not help, I'm not sure what to say, since I've never
fooled around with these settings or had a problem with them. (NOTE: I use
VS2003 .NET, and based my instructions on that, so you may want to ask
someone else if they are slightly different in VS2005 .NET) Good Luck!