I'm debugging an application that is already built, but I do have the pdbs and the source. I just don't have a VC++ project.
I can use the VS 2K5 debugger to step through the code - now I would like to use VA to help me learn the code base. I initiate debugging by opening the .exe file and pressing F5.
Can VA be used to help me understand this code base (via goto def, etc.)?
Not without a solution. VA needs a solution in order to work correctly. Can you try making a "test" solution, by just adding all of the code to a new solution and then running it. If the exe and pdb files are in the correct places you should be able to just tell the IDE to run the program, without trying to compile any of the code.
Once a solution exists VA will parse the files in the solution, and should work normally.