Josh Shepard on Custom Build Steps and Build Events
Josh Shepard continues his discussion of the Visual C++ project system:
to set a custom build step, go to the project properties dialog with either the project or a file selected (depending on whether you want a custom build step at the project-level or file-level), select the "custom build step" node in the left-hand pane and enter the commands you want into the "command line" field. you will also need to set the "output" field to the path to a file that the build step generates. (if there is no value for this property the custom build step will never run). the time-stamp of this output file is checked to see if the custom build step needs to be executed; if the file doesn't exist, the custom build step will always execute. you can also enter "additional dependencies" which are other files that will be time-stamp checked to see if the custom build step is out-of-date and needs to execute.
This is great information. Be sure to check out the whole series on his blog if you get a chance.