Launch Visual Studio .NET 2003. Select Tools | External Tools | Add. Add the settings show below:

Title: ILDASM (or anything else of your choice)

Command: C:\Program Files\Microsoft.NET\SDK\v1.1\Bin\ildasm.exe

Arguments: $(TargetPath)

Initial Directory: $(TargetDir)

Use Output Window: -unchecked-

Prompt for arguments: -unchecked-

Close on exit: -checked-

Contributed from George Shepherd's Windows Forms FAQ