In making a brand new Visual Studio web forms project DevExpress friendly...

1. I brought in the .dlls for DevExpress as references.
    
2. I added this to the system.web chunk of Web.config:
   <compilation debug="true" targetFramework="4.5">
      <assemblies>
         <add assembly="DevExpress.Web.v13.1, Version=13.1.9.0, Culture=neutral,
               PublicKeyToken=B88D1754D700E49A" />
         <add assembly="DevExpress.Data.v13.1, Version=13.1.9.0, Culture=neutral,
               PublicKeyToken=B88D1754D700E49A" />
         <add assembly="DevExpress.Printing.v13.1.Core, Version=13.1.9.0,
               Culture=neutral, PublicKeyToken=B88D1754D700E49A" />
         <add assembly="System.Design, Version=4.0.0.0, Culture=neutral,
               PublicKeyToken=B03F5F7F11D50A3A" />
         <add assembly="System.Windows.Forms, Version=4.0.0.0, Culture=neutral,
               PublicKeyToken=B77A5C561934E089" />
         <add assembly="DevExpress.RichEdit.v13.1.Core, Version=13.1.9.0,
               Culture=neutral, PublicKeyToken=B88D1754D700E49A" />
         <add assembly="System.Data.Linq, Version=4.0.0.0, Culture=neutral,
               PublicKeyToken=B77A5C561934E089" />
         <add assembly="DevExpress.Web.ASPxThemes.v13.1, Version=13.1.9.0,
               Culture=neutral, PublicKeyToken=b88d1754d700e49a" />
      </assemblies>
   </compilation>
    
3. The end of the system.web hunk of Web.config and the whole of the system.webServer stuff ended up looking like this:
      <httpModules>
         <add type="DevExpress.Web.ASPxClasses.ASPxHttpHandlerModule,
               DevExpress.Web.v13.1, Version=13.1.9.0, Culture=neutral,
               PublicKeyToken=b88d1754d700e49a"
               name="ASPxHttpHandlerModule" />
      </httpModules>
      <httpHandlers>
         <add type="DevExpress.Web.ASPxClasses.ASPxHttpHandlerModule,
               DevExpress.Web.v13.1, Version=13.1.9.0, Culture=neutral,
               PublicKeyToken=b88d1754d700e49a" verb="GET" path="DX.ashx"
               validate="false" />
      </httpHandlers>
   </system.web>
   <system.webServer>
      <modules>
         <remove name="FormsAuthenticationModule" />
         <add type="DevExpress.Web.ASPxClasses.ASPxHttpHandlerModule,
               DevExpress.Web.v13.1, Version=13.1.9.0, Culture=neutral,
               PublicKeyToken=b88d1754d700e49a"
               name="ASPxHttpHandlerModule" />
      </modules>
      <validation validateIntegratedModeConfiguration="false" />
      <handlers>
         <add type="DevExpress.Web.ASPxClasses.ASPxHttpHandlerModule,
               DevExpress.Web.v13.1, Version=13.1.9.0, Culture=neutral,
               PublicKeyToken=b88d1754d700e49a" verb="GET" path="DX.ashx"
               name="ASPxHttpHandlerModule" preCondition="integratedMode" />
      </handlers>
   </system.webServer>
    
4. configSections in Web.config was also doctored up in another project I used as a crutch/example, but so far I am doing just fine without that gunk.