debugging methods in C#.net

I want to be able to step through c#.net 2008 code in a project file that is executed as part of the build process. This project file basically gathers all the third party software dlls and and other company dlls into a general bin directory. The project files are in the project properties area on the publish tab and then the application tab. The project file also does performs other activities that I want to step through the code on.
The project file I am referring to is executed in the postbuild command line section of the startup project for the entire .net solution.
I do not know how to step through this code. I was thinking of either:
I was thinking that I could run the lines that are in the postbuild command line in a .net dos prompt. However, I am not certain how I get get the debug options setup. I would want to be able to step through the code like I would user the debugger in the .net framework.
 Do you have any other ideas?

You can Attach the Process through visual studio and then you can easily debug it.
Debug -> Attach to Process -> you can select the process and it will automatically debug your code eventhough its an published one.

I like the idea of attaching to a process. However, do you attach to a process when the command is in the postbuild command line of the build process.
  This code is only executed on a build. Thus can you tell mehow I can attach to a process while it is in the build process?
  thanks!