Philosophlogically Speaking…

There are many ways to run custom code in SharePoint 2007.  Arguably one of the simplest is to create a Custom Application Page, sticking all the source code into a script tag at the top of the page.  You don’t have to muck around with compiling dlls or modifying the web.config file.

1. Create a new aspx file.  Put this at the top:

   
   <%@ Assembly Name="Microsoft.SharePoint, Version=12.0.0.0, Culture=neutral, PublicKeyToken=71E9BCE111E9429C" %>
   <%@ Page language="C#" MasterPageFile="~/_layouts/application.master" Inherits="Microsoft.SharePoint.WebControls.LayoutsPageBase" %>
   

   Watch out! SharePoint Designer likes to remove the ~/ from your MasterPageFile declaration. I have no idea why it does this. I sat there entering it, hitting save, and watching it disappear like 4 times before I opened up Notepad and put it in. Weird.

2. Add any namespaces needed.

   
   <%@ Import Namespace="System" %>
   <%@ Import Namespace="System.Web" %>
   <%@ Import Namespace="System.Web.UI" %>
   

3. Add a script tag (don’t forget to runat server!).

   
   <script runat="server"></script>
   

4. Copy the code from your code-behind and stick it into the shiny new script tag you just created.  Don’t include those pesky namespace or class declarations, just the functions you want.
5. Application Master has some ContentPlaceHolders; we care about three of them. 
   • PlaceHolderMain will hold your tag soup from the ASPX file.
   • PlaceHolderPageTitle will hold the title that shows in the title bar of the browser.
   • PlaceHolderPageTitleInTitleArea holds the page title that goes in the SharePoint chrome (the yellow bar of a typical application page).

   
   <asp:Content ID="Main" contentplaceholderid="PlaceHolderMain" runat="server">
   	<!-- all your aspx content goes here -->
   </asp:Content>
   
   <asp:Content ID="PageTitle" runat="server" contentplaceholderid="PlaceHolderPageTitle">
   	Title in browser title area
   </asp:Content>
   
   <asp:Content ID="PageTitleInTitleArea" runat="server" contentplaceholderid="PlaceHolderPageTitleInTitleArea">
   	Title in SharePoint chrome
   </asp:Content>
   

6. Create a folder in the LAYOUTS virtual directory.  Should be in the C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\12\TEMPLATE\LAYOUTS\ directory.  Don’t ever skip this step! Always separate your grubby code from the pristine beauty of the default code with folders!
7. Copy your newly created .ASPX into the folder created in step 6.
8. Now you can get to your snazzy new Custom Application page in any site by adding /_layouts/PageName.aspx to whatever site you want.
9. There is no step nine.

Have fun!