Hi! I'll try my best to step the process. Please note that isn't probably the only way to do it. It's just how we do.
1. Download the DotNetNuke SOURCE version
2. Unzip it under c:\ or d:\ or whatever preferably not under c:\documents and settings\....
3. Add user ASPNET ACCOUNT and user NETWORK SERVICE to the resulting Website folder (eg. d:\DotNetNuke\Website)
4. Rename release.config to web.config inside the resulting Website folder (eg. d:\DotNetNuke\Website)
5. Open DotNetNuke.sln with Visual Studio 2005 (eg. d:\DotNetNuke\DotNetNuke.sln)
6. Run build all! *(READ NOTES BELOW)
Now depending on which module you want to debug you must add it or not to the solution.
CASE 1:
A module (to make it easy) that resides only under Website/App_Code and Website/DesktopModules can be debugged just open their files and placing a breakpoint.
CASE 2:
A module that resides under Website/bin (here DLL are stored) and Website/DesktopModules need to be added to the solution in order to debug it. Normally the references of the project must be fixed too.
*(Sometimes the build fails because of IIS caching. Start it again with rebuild all)
Hope it helps!
Kind Regards,
D.